Gas oil composition

ABSTRACT

The present invention provides a gas oil composition that can achieve environment load reduction, low temperature properties and low fuel consumption all together and is suitably used in a winter season. The gas oil composition comprises an Ft synthetic base oil in an amount of 60 percent by mass or more on the basis of the total mass of the composition and has a sulfur content of 5 ppm by mass or less, an aromatic content of 10 percent by volume or less, an oxygen content of 100 ppm or less, an end point of 360° C. or lower, an insoluble content after an oxidation stability test of 0.5 mg/100 mL or less, an HFRR wear scar diameter (WS1.4) of 400 μm or smaller and a specific relation in normal paraffin contents and the total content thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 12/295,308filed Sep. 30, 2008, which is a Section 371 of International ApplicationNo. PCT/JP2007/055304, filed Mar. 9, 2007, which was published in theJapanese language on Oct. 11, 2007, under International Publication No.WO 2007/114026 A and the disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to gas oil compositions containing mainlyan FT synthetic base oil, more particularly to gas oil compositions thatcan achieve environment load reduction, low temperature properties andlow fuel consumption all together and are suitably used in a winterseason.

In general, a gas oil composition is produced by blending one or moretypes of base oils produced by subjecting a straight gas oil or straightkerosene, produced by atmospheric distillation of crude oil tohydrorefining or hydrodesulfurization. In particular, it is often thecase that the blend ratio of the foregoing kerosene base oil and gas oilbase oil is adjusted in order to ensure the cold flowability during awinter season. If necessary, the base oils are blended with additivessuch as cetane number improvers, detergents and cold flow improvers(see, for example, Non-Patent Document No. 1 below).

Lower sulfur and aromatic contents are regarded as capable ofsuppressing the formation of harmful components such as NOx and PM inthe exhaust gas from engines. From the view point of this, attention hasbeen brought to fuels such as liquid fractions corresponding to naphtha,kerosene and gas oil, produced by subjecting a mixed gas containingmainly hydrogen and carbon monoxide produced from natural gas, coal,biomass or sludge (hereinafter may be often referred to as “syntheticgas”) to a Fischer-Tropsch (FT) reaction; hydrocarbon mixtures producedby hydrorefining or hydrocracking such liquid fractions; and hydrocarbonmixtures produced by hydrorefining or hydrocracking liquid fractions andFT wax produced through a Fischer-Tropsch reaction, as fuelscontributing environment load reduction.

However, since the FT reaction per se contains a wax formation process,the hydrotreated products of the FT reaction product are relativelylarge in the content of straight-chain saturated hydrocarbon (normalparaffins) compounds. It has been pointed out that in particular whenheavy normal paraffin compounds are contained, there is the possibilitythat they would deposit in the form of wax. Further, the FT syntheticbase oil is a hydrocarbon mixture containing predominantly the aforesaidnormal paraffins and saturated hydrocarbons having a side chain(isoparaffin) and thus is generally poor in oil solubility. Therefore,there is the possibility that additives that are dissolved in fuel oilssuch as gas oil, highly relying on their oil soluble groups(straight-chain alkyl groups or the like) would be hardly dissolved.Among such additives, there would be likely used conventional cold flowimprovers (CFI) composed of an ethylene-vinyl acetate copolymer mixturedue to the restriction on the solubility to fuel.

Patent Document No. 1 discloses in an example thereof a synthetic fuelcontaining a gas oil fraction produced from an FT synthetic base oilonly. However, this gas oil is an extremely light fuel containing akerosene fraction in a large amount because the document intends tosolve a problem concerning low-temperature startability and thus atechnique for improving low-temperature properties with a cold flowimprover can not be selected. As the result, significant reductions indensity, kinematic viscosity and volume calorific value can not beavoided, and furthermore it can not be denied that the reductions wouldresult in significant deterioration in fuel consumption, seizure ofinjection pumps, cavitation damages and defects in high-temperaturerestartability. That is, it is very difficult to design a high-qualityfuel that can achieve at a high level the requirements sought for a gasoil composition having environment load reduction properties, excellentpractical performances in a winter season and suppression of fuelconsumption deterioration all together, and there exists no example orfinding on the basis of studies of such a fuel satisfying variousproperties required for fuel other than the foregoing sufficiently and apractical process for producing the fuel.

-   -   (1) Patent Document No. 1: Japanese Patent Laid-Open Publication        No. 2005-529213    -   (2) Non-Patent Document No. 1: Konishi Seiichi, “Nenryo Kogaku        Gairon”, Shokabo Publishing Co., Ltd., March, 1991, pages 136 to        144

BRIEF SUMMARY OF THE INVENTION

The present invention was made in view of the above-described situationsand has an object to provide a gas oil composition containing mainly anFT synthetic base oil, more specifically such a gas oil composition thatcan achieve environment load reduction, low temperature properties andlow fuel consumption all together and is suitably used in a winterseason.

The present invention was completed as the result of extensive study andresearch carried out by the present inventors to solve the foregoingproblems. That is, the present invention relates to a gas oilcomposition comprising a gas oil composition selected from the groupconsisting of the following gas oil compositions (A) to (C) andadditives added in accordance with the following Steps 1 and 2:

[I] gas oil compositions (A) comprising an FT synthetic base oil in anamount of 60 percent by volume or more on the basis of the total amountof the gas oil composition, with a sulfur content of 5 ppm by mass orless, an aromatic content of 10 percent by volume or less, an oxygencontent of 100 ppm or less, a density of 760 kg/m³ or greater and 840kg/m³ or less, a 90% distillation temperature of 280° C. or higher and330° C. or lower and an end point of 360° C. or lower in distillationcharacteristics, an insoluble content after an oxidation stability testof 0.5 mg/100 mL or less, an HFRR wear scar diameter (WS1.4) of 400 μmor smaller, a cloud point of −15° C. or lower, a cold filter pluggingpoint of −25° C. or lower, a pour point of −32.5° C. or lower, a totalcontent of normal paraffins having 20 to 30 carbon atoms of less than 2percent by mass, a value determined by dividing the total content ofnormal paraffins having 20 to 30 carbon atoms by the total content ofhydrocarbons having 20 to 30 carbon atoms other than the normalparaffins of 0.2 or greater and 0.6 or less, and a relation in thecontent of each of normal paraffins (CnP) having 15 to 20 carbon atomsdefined by C20P<C19P<C18P<C17P<C16P<C15P;

[II] gas oil compositions (B) comprising an FT synthetic base oil in anamount of 60 percent by volume or more on the basis of the total amountof the gas oil composition, with a sulfur content of 5 ppm by mass orless, an aromatic content of 10 percent by volume or less, an oxygencontent of 100 ppm or less, a density of 760 kg/m³ or greater and 840kg/m³ or less, a 90% distillation temperature of 280° C. or higher and350° C. or lower and an end point of 360° C. or lower in distillationcharacteristics, an insoluble content after an oxidation stability testof 0.5 mg/100 mL or less, an HFRR wear scar diameter (WS1.4) of 400 μmor smaller, a cloud point of −5° C. or lower, a cold filter pluggingpoint of −20° C. or lower, a pour point of −25° C. or lower, a totalcontent of normal paraffins having 20 to 30 carbon atoms of 2 percent bymass or more and less than 4 percent by mass, a value determined bydividing the total content of normal paraffins having 20 to 30 carbonatoms by the total content of hydrocarbons having 20 to 30 carbon atomsother than the normal paraffins of 0.2 or greater and 0.6 or less, and arelation in the content of each of normal paraffins (CnP) having 20 to25 carbon atoms defined by C20P>C21P>C22P>C23P>C24P>C25P; and

[III] gas oil compositions (C) comprising an FT synthetic base oil in anamount of 60 percent by volume or more on the basis of the total amountof the gas oil composition, with a sulfur content of 5 ppm by mass orless, an aromatic content of 10 percent by volume or less, an oxygencontent of 100 ppm or less, a density of 760 kg/m³ or greater and 840kg/m³ or less, a 90% distillation temperature of 280° C. or higher and350° C. or lower and an end point of 360° C. or lower in distillationcharacteristics, an insoluble content after an oxidation stability testof 0.5 mg/100 mL or less, an HFRR wear scar diameter (WS1.4) of 400 μmor smaller, a cloud point of −3° C. or lower, a cold filter pluggingpoint of −10° C. or lower, a pour point of −12.5° C. or lower, a totalcontent of normal paraffins having 20 to 30 carbon atoms of 4 percent bymass or more and less than 6 percent by mass, a value determined bydividing the total content of normal paraffins having 20 to 30 carbonatoms by the total content of hydrocarbons having 20 to 30 carbon atomsother than the normal paraffins of 0.2 or greater and 0.6 or less, andrelations in the content of each of normal paraffins (CnP) having 20 to25 carbon atoms defined by C20P>C21P>C22P>C23P>C24P>C25P and(C24P-C25P)/C24P>(C22P-C23P)/C22P>(C20P-C21P)/C20P;

(Step 1) a lubricity improver comprising a fatty acid and/or a fattyacid ester is admixed in an amount of 20 mg/L or more and 300 mg/L orless in terms of the active component with the gas oil composition byline-blending, forced-stirring or leaving to stand for a sufficienttime; and

(Step 2) a cold flow improver comprising an ethylene vinyl acetatecopolymer and/or a compound with a surface active effect is admixed inan amount of 20 mg/L or more and 1000 mg/L or less in terms of theactive component with the gas oil composition by line-blending,forced-stirring or leaving to stand for a sufficient time.

Alternatively, the gas oil composition of the present invention ispreferably admixed with 200 mg/L or more and 500 mg/L or less of adetergent comprising a polyether amine compound, a polybutenyl aminecompound, an alkenyl succinamide compound, or an alkenyl succinimidecompound by line-blending, forced-stirring or leaving to stand for asufficient time, in a step added between Steps 1 and 2. Preferably, thelubricity improver, detergent and cold flow improver each contain asolvent containing no chemical substance with a melting point of 10° C.or higher. Preferably, the gas oil composition has a peroxide numberafter an accelerated oxidation test of 50 ppm by mass or less, akinematic viscosity at 30° C. of 2.5 mm²/s or greater and 5.0 mm²/s orless, a cetane index of 45 or greater and a water content of 100 ppm byvolume or less.

The intentions of the present invention are as follows. A fuel would beadversely affected if it is produced by a process wherein the waxcontent is extremely reduced by excessive lightening, and a fuel of lowoil solubility, which is produced solely from an FT synthetic base oilwould hardly dissolve additives, resulting in the possibility that theywould fail to exhibit their original advantageous effects. Therefore,the present invention is intended to create and propose a quality designmethod required for imparting a fuel reduced in oil solubility with aneffect to improve cold flowability by addition of additives such as CFI.

According to the present invention, the use of a gas oil compositionproduced by the above-described process to satisfy the above-describedrequirements regarding fractions and the like renders it possible toproduce easily a gas oil composition suitable for a winter season thatcan achieve environment load reduction, low-temperature properties andlow fuel consumption all together, which have been difficult to achievewith the conventional gas oil compositions.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown.

In the drawings:

FIG. 1 is a diagram illustrating a over driving mode simulating a realrun.

DETAILED DESCRIPTION OF THE INVENTION

The gas oil composition of the present invention necessarily contains anFT synthetic base oil. The FT synthetic base oil is composed ofsaturated hydrocarbon compounds, and the gas oil composition of thepresent invention can be easily produced by adjusting the blend of thehydrocarbon compounds. There is no particular restriction on thecharacteristics of the FT synthetic base oil as long as thecharacteristics of the gas oil composition of the present invention aresatisfied. There is no particular restriction on base oils other thanthe FT synthetic base oil as long as the characteristics of the gas oilcomposition of the present invention are fulfilled. However, in order toallow the composition to exhibit sufficient environment friendlyproperties, it is preferable to blend the following petroleum base oilhaving been highly hydrotreated and animal- or vegetable-derivedprocessed oils.

The FT synthetic base oil referred herein denotes various synthetic oilssuch as liquid fractions corresponding to naphtha, kerosene and gas oil,produced by subjecting a mixed gas containing mainly hydrogen and carbonmonoxide (hereinafter may be often referred to as “synthetic gas”) to aFischer-Tropsch (FT) reaction; hydrocarbon mixtures produced byhydrorefining or hydrocracking such liquid fractions; and hydrocarbonmixtures produced by hydrorefining or hydrocracking liquid fractions andFT wax produced through a Fischer-Tropsch reaction.

The gas oil composition comprises preferably 60 percent by volume ormore of the FT synthetic base oil. Further, the composition comprisesmore preferably 70 percent by volume or more, more preferably 80 percentby volume or more of the FT synthetic base oil with the objective oflessening the occasion to increase the burden to the environment causedby sulfur components or aromatic components.

The mixed gas which will be the feedstock of the FT synthetic oil isproduced by oxidizing a substance containing carbon using oxygen and/orwater and/or carbon dioxide as an oxidizing agent and further ifnecessary by a shift reaction using water so as to be adjusted inpredetermined hydrogen and carbon monoxide concentrations.

Substances containing carbon which may be used herein are generally gascomponents composed of hydrocarbons that are gas in normal temperaturessuch as natural gas, liquefied petroleum gas, and methane gas, petroleumasphalt, biomass, coke, wastes such as building materials and garbage,sludge, heavy crude oils that are difficult to be disposed in the usualmanner, and mixed gas produced by exposing unconventional petroleumresources to elevated temperatures. However, in the present invention,there is no particular restriction on the feedstock as long as a mixedgas containing mainly hydrogen and carbon monoxide can be produced.

The Fischer-Tropsch reaction requires a metal catalyst. It is preferableto use metals in Group 8 of the periodic table, such as cobalt,ruthenium, rhodium, palladium, nickel and iron, more preferably metalsin Group 8, Period 4, as an active catalyst component. Alternatively,there may be used a mixed metal group containing these metals insuitable amounts. These active metals are generally used in the form ofa catalyst produced by supporting them on a support such as alumina,titania and silica-alumina. Alternatively, the use of the forgoingactive metals in combination with a second metal can improve theperformances of the resulting catalyst. Examples of the second metalinclude alkali or alkaline earth metals such as sodium, lithium andmagnesium, zirconium, hafnium and titanium, which will be used dependingon purposes such as increase in conversion rate of carbon monoxide orchain growth probability (a) which is an index of the production amountof wax.

The Fischer-Tropsch reaction is a synthetic method for producing liquidfractions and FT wax using a mixed gas as the feedstock. It is generallypreferable to adjust the ratio of hydrogen to carbon monoxide in themixed gas in order to carry out the synthetic method efficiently. Ingeneral, the molar mix ratio of hydrogen to carbon monoxide(hydrogen/carbon monoxide) is preferably 1.2 or greater, more preferably1.5 or greater, more preferably 1.8 or greater. The ratio is alsopreferably 3 or less, more preferably 2.6 or less, more preferably 2.2or less.

The reaction temperature at which the Fischer-Tropsch reaction iscarried out using the foregoing catalyst is preferably 180° C. or higherand 320° C. or lower, more preferably 200° C. or higher and 300° c. orlower. At a reaction temperature of lower than 180° C., carbon monoxidehardly reacts, resulting in a tendency that the hydrocarbon yield isreduced. At a reaction temperature of higher than 320° C., gas such asmethane is increasingly formed, resulting in a reduction in theproduction efficiency of liquid fractions and FT wax.

There is no particular restriction on the gas hourly space velocity withrespect to the catalyst. However, it is preferably 500 h⁻¹ or more and4000 h⁻¹ or lower, more preferably 1000 h⁻¹ or more and 3000 h⁻¹ orlower. A gas hourly space velocity of less than 500 h⁻¹ is likely toreduce the production of the liquid fuel while a gas hourly spacevelocity of more than 400 h⁻¹ causes a necessity to increase thereaction temperature and increase the amount of gas to be produced,resulting in a reduction in the yield of the intended product.

There is no particular restriction on the reaction pressure (partialpressure of a synthetic gas composed of carbon monoxide and hydrogen).However, it is preferably 0.5 MPa or greater and 7 MPa or smaller, morepreferably 2 MPa or greater and 4 MPa or smaller. If the reactionpressure is smaller than 0.5 MPa, the yield of liquid fuel would tend todecrease. If the reaction pressure is greater than 7 MPa, it is noteconomically advantageous because the amount of capital investment infacilities would be increased.

If necessary, liquid fractions and FT wax produced through theabove-described FT reaction may be hydrorefined or hydrocracked in anysuitable manner so as to be adjusted in distillation characteristics orcomposition to achieve the purposes of the invention. Hydrorefining orhydrocracking may be selected depending on the purposes and the presentinvention is not limited in selection to either one or both of them tosuch an extent that the gas oil composition of the present invention isproduced.

Catalysts used for hydrorefining are generally those comprising ahydrogenation active metal supported on a porous support, but thepresent invention is not limited thereto as long as the same effects areobtained.

The porous support is preferably an inorganic oxide. Specific examplesinclude alumina, titania, zirconia, boria, silica, zeolite and the like.

Zeolite is crystalline aluminosilicate, examples of which includefaujasite, pentasil and mordenite type zeolites. Preferred arefaujasite, beta and mordenite type zeolites and particularly preferredare Y-type and beta-type zeolites. Y-type zeolites are preferably ultrastable.

Preferred for the active metal are those of the following two types(active metal A type and active metal B type).

The active metal A type is at least one type of metal selected from thegroup consisting of those in Group 8 of the periodic table. It ispreferably at least one type selected from the group consisting of Ru,Rh, Ir, Pd and Pt, and is more preferably Pd and/or Pt. The active metalmay be a combination of these metals, such as Pt—Pd, Pt—Rh, Pt—Ru,Ir—Pd, Ir—Rh, Ir—Ru, Pt—Pd—Rh, Pt—Rh—Ru, Ir—Pd—Rh, and Ir—Rh—Ru. A noblemetal catalyst formed of these metals can be used after being subjectedto a pre-reduction treatment under hydrogen flow. In general, thecatalyst is heated at a temperature of 200° C. or higher in accordancewith predetermined procedures, circulating a gas containing hydrogen sothat the active metal on the catalyst is reduced and thus exhibitshydrogenation activity.

The active metal B type contains preferably at least one type of metalselected from the group consisting of those in Groups 6A and 8 of theperiodic table, desirously two or more types of metals selectedtherefrom. Examples of these metals include Co—Mo, Ni—Mo, Ni—Co—Mo andNi—W. When a metal sulfide catalyst formed of these metals is used, itmust undergo a pre-sulfurization process.

The metal source may be a conventional inorganic salt or complex saltcompound. The supporting method may be any supporting method that hasbeen usually used for hydrogenation catalysts, such as impregnation andion-exchange methods. When a plurality of metals are supported, they maybe supported simultaneously using a mixed solution thereof orsequentially using a single solution containing each metal. The metalsolution may be an aqueous solution or a solution using an organicsolvent.

The reaction temperature at which hydrorefining is carried out using acatalyst composed of the active metal A type is preferably 180° C. orhigher and 400° C. or lower, more preferably 200° C. or higher and 370°C. or lower, more preferably 250° C. or higher and 350° C. or lower,more preferably 280° C. or higher and 350° C. or lower. A reactiontemperature of higher than 370° C. is not preferable because the yieldof the middle fraction is extremely reduced, resulting from an increasein a side reaction wherein the liquid fraction or FT wax is cracked to anaphtha fraction. A reaction temperature of lower than 270° C. is notalso preferable because alcohols can not be removed and thus remains inthe reaction system.

The reaction temperature at which hydrorefining is carried out using acatalyst composed of the active metal B type is preferably 170° C. orhigher and 320° C. or lower, more preferably 175° C. or higher and 300°C. or lower, more preferably 180° C. or higher and 280° C. or lower. Areaction temperature of higher than 320° C. is not preferable becausethe yield of the middle fraction is reduced, resulting from an increasein a side reaction wherein the liquid fraction or FT wax is cracked to anaphtha fraction. A reaction temperature of lower than 170° C. is notalso preferable because alcohols can not be removed and thus remains inthe reaction system.

The hydrogen pressure at which hydrorefining is carried out using acatalyst composed of the active metal A type is preferably 0.5 MPa orgreater and 12 MPa or less, more preferably 1.0 MPa or greater and 5.0MPa or less. Although a higher hydrogen pressure facilitates thehydrogenation reaction, there is generally an optimum point ineconomical sense.

The hydrogen pressure at which hydrorefining is carried out using acatalyst composed of the active metal B type is preferably 2 MPa orgreater and 10 MPa or less, more preferably 2.5 MPa or greater and 8 MPaor less, more preferably 3 MPa or greater and 7 MPa or less. Although ahigher hydrogen pressure facilitates the hydrogenation reaction, thereis generally an optimum point in economical sense.

The liquid hourly space velocity (LHSV) at which hydrorefining iscarried out using a catalyst composed of the active metal A type ispreferably 0.1 h⁻¹ or greater and 10.0 h⁻¹ or less, more preferably 0.3h⁻¹ or greater and 3.5 h⁻¹ or less. Although a lower LHSV isadvantageous for the reaction, a too low LHSV is not economicallypreferable because it requires an extremely large reactor volume,leading to an excessive capital investment in facilities.

The liquid hourly space velocity (LHSV) at which hydrorefining iscarried out using a catalyst composed of the active metal B type ispreferably 0.1 h⁻¹ or greater and 2 h⁻¹ or less, more preferably 0.2 h⁻¹or greater and 1.5 h⁻¹ or less, more preferably 0.3 h⁻¹ or greater and1.2 h⁻¹ or less. Although a lower LHSV is advantageous for the reaction,a too low LHSV is not economically preferable because it requires anextremely large reactor volume, leading to an excessive capitalinvestment in facilities.

The hydrogen/oil ratio at which hydrorefining is carried out using acatalyst composed of the active metal A type is preferably 50 NL/L orgreater and 1000 NL/L or less, more preferably 70 NL/L or greater and800 NL/L or less. Although a higher hydrogen/oil ratio facilitates thereaction, there is generally an optimum point in economical sense.

The hydrogen/oil ratio at which hydrorefining is carried out using acatalyst composed of the active metal B type is preferably 100 NL/L orgreater and 800 NL/L or less, more preferably 120 NL/L or greater and600 NL/L or less, more preferably 150 NL/L or greater and 500 NL/L orless. Although a higher hydrogen/oil ratio facilitates the reaction,there is generally an optimum point in economical sense.

Catalysts used for hydrocracking are generally those comprising ahydrogenation active metal supported on a support with solid acidicproperties, but the present invention is not limited thereto as long asthe same effects are obtained.

As for the support with solid acidic properties, there are amorphous andcrystalline zeolite types. Specific examples include silica-alumina,silica-magnesia, silica-zirconia and silica-titania, which are ofamorphous type and zeolites of faujasite, beta, MFI and mordenite types,preferably Y type and beta type. The Y type zeolites are preferablythose that are ultra stable.

Preferred for the active metal are those of the following two types(active metal A type and active metal B type).

The active metal A type is at least one type of metal mainly selectedfrom the group consisting of those in Groups 6A and 8 of the periodictable. It is preferably at least one type of metal selected from thegroup consisting of Ni, Co, Mo, Pt, Pd and W. A noble metal catalystformed of these metals can be used after being subjected to apre-reduction treatment under hydrogen flow. In general, the catalyst isheated at a temperature of 200° C. or higher in accordance withpredetermined procedures, circulating a gas containing hydrogen so thatthe active metal on the catalyst is reduced and thus exhibitshydrogenation activity.

The active metal B type may be a combination of these metals, such asPt—Pd, Co—Mo, Ni—Mo, Ni—W, and Ni—Co—Mo. When a catalyst formed of thesemetals is used, it must undergo a pre-sulfurization process before use.

The metal source may be a conventional inorganic salt or complex saltcompound. The supporting method may be any supporting method that hasbeen usually used for hydrogenation catalysts, such as impregnation andion-exchange methods. When a plurality of metals are supported, they maybe supported simultaneously using a mixed solution thereof orsequentially using a single solution containing each metal. The metalsolution may be an aqueous solution or a solution with an organicsolvent.

The reaction temperature at which hydrocracking is carried out using acatalyst composed of the active metal type A and active metal type B ispreferably 200° C. or higher and 450° C. or lower, more preferably 250°C. or higher and 430° C. or lower, more preferably 300° C. or higher and400° C. or lower. A reaction temperature of higher than 450° C. is notpreferable because the yield of the middle fraction is extremelyreduced, resulting from an increase in a side reaction wherein theliquid fraction or FT wax is cracked to a naphtha fraction. A reactiontemperature of lower than 200° C. is not also preferable because theactivity of the catalyst is extremely reduced.

The hydrogen pressure at which hydrocracking is carried out using acatalyst composed of the active metal type A and active metal type B ispreferably 1 MPa or greater and 20 MPa or less, more preferably 4 MPa orgreater and 16 MPa or less, more preferably 6 MPa or greater and 13 MPaor less. Although a higher hydrogen pressure facilitates thehydrogenation reaction, the cracking reaction would rather proceedslowly and thus needs to be adjusted in the proceeding thereof byincreasing the reaction temperature, leading to a short working life ofthe catalyst. Therefore, there is generally an optimum point ineconomical sense.

The liquid hourly space velocity (LHSV) at which hydrocracking iscarried out using a catalyst composed of the active metal A type ispreferably 0.1 h⁻¹ or greater and 10.0 h⁻¹ or less, more preferably 0.3h⁻¹ or greater and 3.5 h⁻¹ or less. Although a lower LHSV isadvantageous for the reaction, a too low LHSV is not economicallypreferable because it requires an extremely large reactor volume,leading to an excessive capital investment in facilities.

The liquid hourly space velocity (LHSV) at which hydrocracking iscarried out using a catalyst composed of the active metal B type ispreferably 0.1 h⁻¹ or greater and 2 h⁻¹ or less, more preferably 0.2 h⁻¹or greater and 1.7 h⁻¹ or less, more preferably 0.3 h⁻¹ or greater and1.5 h⁻¹ or less. Although a lower LHSV is advantageous for the reaction,a too low LHSV is not economically preferable because it requires anextremely large reactor volume, leading to an excessive capitalinvestment in facilities.

The hydrogen/oil ratio at which hydrocracking is carried out using acatalyst composed of the active metal A type is preferably 50 NL/L orgreater and 1000 NL/L or less, more preferably 70 NL/L or greater and800 NL/L or less, more preferably 400 NL/L or greater and 1500 NL/L orless. Although a higher hydrogen/oil ratio facilitates the reaction,there is generally an optimum point in economical sense.

The hydrogen/oil ratio at which hydrocracking is carried out using acatalyst composed of the active metal B type is preferably 150 NL/L orgreater and 2000 NL/L or less, more preferably 300 NL/L or greater and1700 NL/L or less, more preferably 400 NL/L or greater and 1500 NL/L orless. Although a higher hydrogen/oil ratio facilitates the reaction,there is generally an optimum point in economical sense.

The reactor for hydrogenation may be of any structure and a single or aplurality of reaction tower may be used. Hydrogen may be additionallysupplied between a plurality of reaction towers. The reactor may have afacility for removing sulfurized hydrogen and a distillation tower forfractionally distilling hydrogenated products for producing desiredfractions.

The reaction mode of the hydrogenation reactor may be a fixed bed mode.Hydrogen may be supplied to the feedstock in a counter or parallel flowmode. Alternatively, the reaction mode may be a combination of counterand parallel flow modes, with a plurality of reaction towers. The supplymode of the feedstock is generally down flow and is preferably agas-liquid cocurrent flow mode. Hydrogen gas may be supplied as quencherinto a middle portion of a reactor for the purposes of removing thereaction heat or increasing the hydrogen partial pressure.

The above-mentioned petroleum-based base oil is a hydrocarbon base oilproduced by processing crude oil. Examples include straight base oilsproduced through an atmospheric distillation unit; vacuum base oilsproduced by processing straight heavy oil or residue produced through anatmospheric distillation unit, in a vacuum distillation unit;catalytically cracked or hydrocracked base oils produced bycatalytically cracking or hydrocracking vacuum heavy base oil ordesulfurized fuel oil; and hydrorefined or hydrodesulfurized base oilsproduced by hydrorefining any of these petroleum hydrocarbons.Alternatively, other than crude oil, base oils produced by subjecting toresources referred to as unconventional petroleum resources, such as oilshale, oil sand and Orinoco tar to suitable processing to haveproperties equivalent to those of the foregoing base oils may be used asthe base oil in the present invention.

The above-mentioned highly hydrogenated petroleum-based base oil is akerosene or gas oil fraction produced by hydrorefining and thenhydrotreating a predetermined feedstock. Examples of the feedstockinclude straight kerosene or gas oils produced through an atmosphericdistillation unit for crude oil; vacuum kerosene or gas oils produced byprocessing straight heavy oil or residue produced through an atmosphericdistillation unit, in a vacuum distillation unit; and hydrorefined andhydrodesulfurized kerosene or gas oils produced by hydrotreatingcatalytically cracked kerosene or gas oils produced by catalyticallycracking desulfurized or undesulfurized vacuum kerosene or gas oils,vacuum heavy gas oil or desulfurized fuel oil.

When the feedstock is a gas oil fraction, conditions for hydrorefiningmay be those determined when a hydrodesulfurizing unit is generally usedfor petroleum refining. Generally, hydrorefining of a gas oil fractionis carried out under conditions where the reaction temperature is from300 to 380° C., the hydrogen pressure is from 3 to 8 MPa, the LHSV isfrom 0.3 to 2 h⁻¹, and the hydrogen/oil ratio is from 100 to 500 NL/L.When the feedstock is a kerosene fraction, conditions for hydrorefiningmay be those determined when a hydrodesulfurizing unit is generally usedfor petroleum refining. Generally, hydrorefining of a kerosene fractionis carried out under conditions where the reaction temperature is from220 to 350° C., the hydrogen pressure is from 1 to 6 MPa, the LHSV isfrom 0.1 to 10 h⁻¹, and the hydrogen/oil ratio is from 10 to 300 NL/L,preferably conditions where the reaction temperature is from 250 to 340°C., the hydrogen pressure is from 2 to 5 MPa, the LHSV is from 1 to 10h⁻¹, and the hydrogen/oil ratio is from 30 to 200 NL/L, more preferablyunder conditions where the reaction temperature is from 270 to 330° C.,the hydrogen pressure is from 2 to 4 MPa, the LHSV is from 2 to 10 h⁻¹,and the hydrogen/oil ratio is from 50 to 200 NL/L.

A lower reaction temperature is advantageous for hydrogenation reactionbut is not preferable for desulfurization reaction. A higher hydrogenpressure and a higher hydrogen/oil ratio facilitate desulfurization andhydrogenation reactions but there is an optimum point in economicalsense. Although a lower LHSV is advantageous for the reaction, a too lowLHSV is not economically preferable because it requires an extremelylarge reactor volume, leading to an excessive capital investment infacilities.

A catalyst used for the hydrorefining may be any of the conventionalhydrodesulfurization catalysts. Preferably, the active metals of thecatalyst are the Groups 6A and 8 metals of the periodic table. Examplesof these metals include Co—Mo, Ni—Mo, Co—W, and Ni—W. The support may bean porous inorganic oxide containing alumina as the main component.These conditions and the catalyst are not particularly restricted aslong as the characteristics of the feedstock are satisfied.

The feedstock used in the present invention is produced through theabove-described hydrorefining process and has preferably a sulfurcontent of 5 ppm by mass or more and 10 ppm by mass or less and aboiling point of 130° C. or higher and 380° C. or lower. The feed stockhaving a sulfur content and a boiling point within these ranges canensure the easy achievement of the characteristics defined for thefollowing high hydrogenation process.

The highly hydrotreated base oil is produced by hydrotreating theabove-described hydrogenated kerosene or gas oil as the feedstock in thepresence of a hydrogenation catalyst.

Conditions for the highly hydrogenation are those where the reactiontemperature is from 170 to 320° C., the hydrogen pressure is from 2 to10 MPa, the LHSV is from 0.1 to 2 h⁻¹, and the hydrogen/oil ratio isfrom 100 to 800 NL/L, preferably conditions where the reactiontemperature is from 175 to 300° C., the hydrogen pressure is from 2.5 to8 MPa, the LHSV is from 0.2 to 1.5 h⁻¹, and the hydrogen/oil ratio isfrom 150 to 600 NL/L, more preferably under conditions where thereaction temperature is from 180 to 280° C., the hydrogen pressure isfrom 3 to 7 MPa, the LHSV is from 0.3 to 1.2 h⁻¹, and the hydrogen/oilratio is from 150 to 500 NL/L. A lower reaction temperature isadvantageous for hydrogenation reaction but is not preferable fordesulfurization reaction. A higher hydrogen pressure and a higherhydrogen/oil ratio facilitate desulfurization and hydrogenationreactions but there is an optimum point in economical sense. Although alower LHSV is advantageous for the reaction, a too low LHSV is noteconomically preferable because it requires an extremely large reactorvolume, leading to an excessive capital investment in facilities.

A unit for hydrotreating the feedstock having been hydrorefined may beof any structure, and a single or a plurality of reactors in combinationmay be used. Hydrogen may be additionally introduced into the spacesbetween a plurality of reactors. The hydrorefining unit may be providedwith a gas-liquid separation system or a hydrogen sulfide removalsystem.

The reaction mode of the hydrogenation reactor may be a fixed bed mode.Hydrogen may be supplied to the feedstock in a counter or parallel flowmode. Alternatively, the reaction mode may be a combination of counterand parallel flow modes, with a plurality of reaction towers. The supplymode of the feedstock is generally down flow and is preferably agas-liquid cocurrent flow mode. Hydrogen gas may be supplied as quencherinto a middle portion of a reactor for the purposes of removing thereaction heat or increasing the hydrogen partial pressure.

A catalyst used for hydrotreating comprises a hydrogenation active metalsupported on a porous support. The porous support may be an inorganicoxide such as alumina. Examples of the inorganic oxide include alumina,titania, zirconia, boria, silica, and zeolite. In the present invention,the support is preferably composed of alumina and at least one selectedfrom titania, zirconia, boria, silica, and zeolite. There is noparticular restriction on the method of producing the support.Therefore, there may be employed any method using raw materials in theform of sols or salt compounds each containing any of the elements.Alternatively, the support may be prepared by forming a complexhydroxide or oxide such as silica alumina, silica zirconia, aluminatitania, silica titania, and alumina boria and then adding at any stepalumina in the form of alumina gel, a hydroxide, or a suitable solution.Alumina can be contained in any ratio to the other oxides on the basisof the porous support. However, the content of alumina is preferably 90percent by mass or less, more preferably 60 percent by mass or less, andmore preferably 40 percent by mass or less, of the mass of the poroussupport.

Zeolite is a crystalline alumino silicate. Examples of the crystallinestructure include faujasite, pentasil, and mordenite. These zeolites maybe those ultra-stabilized by a specific hydrothermal treatment and/oracid treatment or those whose alumina content is adjusted. Preferredzeolites are those of faujasite, beta and mordenite types, andparticularly preferred zeolites are those of Y and beta types. Thezeolites of Y type are preferably ultra-stabilized. The ultra-stabilizedzeolite have a micro porous structure peculiar thereto, so-called micropores of 20 Å or smaller and also newly formed pores in the range of 20to 100 Å. The hydrothermal treatment may be carried out under knownconditions.

The active metal of the catalyst used for hydrotreating is at least onemetal selected from the Group 8 metals of the periodic table, preferablyat least one metal selected from Ru, Rh, Ir, Pd, and Pt, and morepreferably Pd and/or Pt. These metals may be used in combination such asPt—Pd, Pt—Rh, Pt—Ru, Ir—Pd, Ir—Rh, Ir—Ru, Pt—Pd—Rh, Pt—Rh—Ru, Ir—Pd—Rh,and Ir—Rh—Ru. The metal sources of these metals may be inorganic saltsor complex salt compounds which have been conventionally used. Themethod of supporting the metal may be any of methods such as immersionand ion exchange which are used for a hydrogenation catalyst. When aplurality of metals are supported, they may be supported using a mixedsolution thereof at the same time. Alternatively, a plurality of metalsmay be supported using solutions each containing any of the metals oneafter another. These metal solutions may be aqueous solutions or thoseproduced using an organic solvent.

The metal(s) may be supported on the porous support after completion ofall the steps for preparing the porous support. Alternatively, themetal(s) may be supported on the porous support in the form of asuitable oxide, complex oxide or zeolite produced at the intermediatestage of the preparation of the porous support and then may proceed togel-preparation or be subjected to heat-concentration and kneading.

There is no particular restriction on the amount of the active metal(s)to be supported. However, the amount is from 0.1 to 10 percent by mass,preferably from 0.15 to 5 percent by mass, and more preferably from 0.2to 3 percent by mass on the basis of the catalyst mass.

The catalyst is preferably used after it is subjected to a pre-reductiontreatment under a hydrogen stream. In general, the active metal(s) aresubjected to heat at 200° C. or higher in accordance with thepredetermined procedures, circulating gas containing hydrogen and thenreduced, thereby exerting catalytic activity.

The animal- or vegetable-derived processed oils referred above are baseoils composed of hydrocarbons produced by applying chemical reactionprocesses applied to produce the above-described petroleum-based baseoils, to oils or fats yielded or produced animal or vegetable rawmaterials. More specifically, the animal- or vegetable-derived processedoils are hydrocarbon-containing mixed base oils produced by contactingan animal or vegetable fat and a component derived therefrom used as afeedstock with a hydrocracking catalyst containing at least one or moremetals selected from the Groups 6A and 8 metals of the periodic tableand an inorganic oxide with acidic properties, under hydrogen pressure.The feedstock of the animal- or vegetable-derived processed oil isnecessarily an animal or vegetable fat or a component derived therefrom.Examples of the animal or vegetable fat or the component originatingtherefrom used herein include natural or artificially made or producedanimal or vegetable fats and animal or vegetable fat componentsoriginating therefrom. Examples of raw materials of the animal fats andanimal oils include beef tallow, milk fat (butter), lard, mutton tallow,whale oil, fish oil, and liver oil. Examples of raw materials of thevegetable fats and vegetable oils include the seeds and other parts ofcoconut, palm tree, olive, safflower, rape (rape blossoms), rice bran,sunflower, cotton seed, corn, soy bean, sesame, and flaxseed. Fats oroils other than those produced from these materials may also be used inthe present invention. The feedstocks may be of solid or liquid but arepreferably produced from vegetable fats or vegetable oils with theobjective of easy handling, carbon dioxide absorptivity, and highproductivity. Alternatively, waste oils resulting from the use of theseanimal and vegetable oils for household, industry and food preparationpurposes may be used as the feedstock after the residual matters areremoved from these oils.

Examples of the typical composition of the fatty acid part of theglyceride compounds contained in these feedstocks include fatty acids,so-called saturated fatty acids having no unsaturated bond in themolecules, such as butyric acid (C₃H₇COOH), caproic acid (C₅H₁₁COOH),caprylic acid (C₇H₁₅COOH), capric acid (C₉H₁₉COOH), lauric acid(C₁₁H₂₃COOH), myristic acid (C₁₃H₂₇COOH), palmitic acid (C₁₅H₃₁COOH),stearic acid (C₁₇H₃₅COOH), and so-called unsaturated fatty acids havingone or more unsaturated bonds in the molecules, such as oleic acid(C₁₇H₃₃COOH), linoleic acid (C₁₇H₃₁COOH), linolenic acid (C₁₇H₂₉COOH)and ricinoleic acid (C₁₇H₃₂(OH)COOH). In general, the hydrocarbon partsof these fatty acids contained in substances existing in nature aremostly of straight chain. However, the fatty acid may be any of thosehaving a side chain structure, i.e., isomers as long as the propertiesdefined by the present invention are satisfied. The unsaturated fattyacid may be any of those existence of which are generally recognized innature as well as those having an unsaturated bond per molecule, theposition of which is adjusted through chemical synthesis as long as theproperties defined by the present invention are satisfied.

The above-described feedstocks (animal or vegetable fats and componentsderived therefrom) contain one or more of these fatty acids, which varydepending on the raw materials. For example, coconuts oil contains arelatively large amount of saturated fatty acids such as lauric acid andmyristic acid while soy bean oil contains a large amount of unsaturatedfatty acids such as oleic acid and linoleic acid.

The feedstock contains a fraction whose boiling point is preferably 250°C. or higher, more preferably a fraction whose boiling point is 300° C.or higher, and more preferably a fraction whose boiling point is 360° C.or higher. If the feedstock contains no fraction whose boiling point is230° C. or higher, the yield of a liquid product would be decreased dueto an increase in gas formed during the production, possibly resultingin an increase in life cycle carbon dioxide.

Alternatively, the feedstock of the animal or vegetable-derivedprocessed oil may be a mixture of an animal or vegetable fat and acomponent derived therefrom, with a petroleum hydrocarbon fraction. Inthis case, the ratio of the petroleum hydrocarbon fraction is preferablyfrom 10 to 99 percent by volume, more preferably from 30 to 99 percentby volume, and more preferably from 60 to 98 percent by volume, of thetotal volume of the feedstock. If the ratio is less than the lowerlimit, there may arise the necessity of facilities for disposal ofby-produced water. If the ratio exceeds the upper limit, it is notpreferable in view of life cycle carbon dioxide reduction.

Conditions of hydrocracking the feedstock during the hydrotreating arethose desirously wherein the hydrogen pressure is from 6 to 20 MPa, theliquid hourly space velocity (LHSV) is from 0.1 to 1.5 h⁻¹, and thehydrogen/oil ratio is from 200 to 2000 NL/L, more desirously wherein thehydrogen pressure is from 8 to 17 MPa, the liquid hourly space velocity(LHSV) is from 0.2 to 1.1 h⁻¹, and the hydrogen/oil ratio is from 300 to1800 NL/L, more desirously wherein the hydrogen pressure is from 10 to16 MPa, the liquid hourly space velocity (LHSV) is from 0.3 to 0.9 h⁻¹,and the hydrogen/oil ratio is from 350 to 1600 NL/L. Each of theconditions is a factor exerting an influence on the reaction activity.For example, if the hydrogen pressure and hydrogen/oil ratio are lessthan the lower limits, the reactivity tends to reduce, and the activitytends to reduce rapidly. If the hydrogen pressure and hydrogen/oil ratioexceed the upper limits, an enormous plant investment for a compressormay be required. A lower liquid hourly space velocity tends to be moreadvantageous for the reactions. However, if the liquid hourly spacevelocity is lower than 0.1 h⁻¹, an enormous plant investment forconstruction of a reactor with an extremely large volume may berequired. If the liquid hourly space velocity exceeds 1.5 h⁻¹, thereaction tends to proceed insufficiently.

The gas oil composition of the present invention necessarily containsmainly an FT synthetic base oil and has the characteristics describedbelow.

The gas oil composition of the present invention comprises a gas oilcomposition selected from the group consisting of the following gas oilcompositions (A) to (C) and additives added in accordance with thefollowing Steps 1 and 2:

[I] gas oil compositions (A) comprising an FT synthetic base oil in anamount of 60 percent by volume or more on the basis of the total amountof the gas oil composition, with a sulfur content of 5 ppm by mass orless, an aromatic content of 10 percent by volume or less, an oxygencontent of 100 ppm or less, a density of 760 kg/m³ or greater and 840kg/m³ or less, a 90% distillation temperature of 280° C. or higher and330° C. or lower and an end point of 360° C. or lower in distillationcharacteristics, an insoluble content after an oxidation stability testof 0.5 mg/100 mL or less, an HFRR wear scar diameter (WS1.4) of 400 μmor smaller, a cloud point of −15° C. or lower, a cold filter pluggingpoint of −25° C. or lower, a pour point of −32.5° C. or lower, a totalcontent of normal paraffins having 20 to 30 carbon atoms of less than 2percent by mass, a value determined by dividing the total content ofnormal paraffins having 20 to 30 carbon atoms by the total content ofhydrocarbons having 20 to 30 carbon atoms other than the normalparaffins of 0.2 or greater and 0.6 or less, and a relation in thecontent of each of normal paraffins (CnP) having 15 to 20 carbon atomsdefined by C20P<C19P<C18P<C17P<C16P<C15P;

[II] gas oil compositions (B) comprising an FT synthetic base oil in anamount of 60 percent by volume or more on the basis of the total amountof the gas oil composition, with a sulfur content of 5 ppm by mass orless, an aromatic content of 10 percent by volume or less, an oxygencontent of 100 ppm or less, a density of 760 kg/m³ or greater and 840kg/m³ or less, a 90% distillation temperature of 280° C. or higher and350° C. or lower and an end point of 360° C. or lower in distillationcharacteristics, an insoluble content after an oxidation stability testof 0.5 mg/100 mL or less, an HFRR wear scar diameter (WS1.4) of 400 μmor smaller, a cloud point of −5° C. or lower, a cold filter pluggingpoint of −20° C. or lower, a pour point of −25° C. or lower, a totalcontent of normal paraffins having 20 to 30 carbon atoms of 2 percent bymass or more and less than 4 percent by mass, a value determined bydividing the total content of normal paraffins having 20 to 30 carbonatoms by the total content of hydrocarbons having 20 to 30 carbon atomsother than the normal paraffins of 0.2 or greater and 0.6 or less, and arelation in the content of each of normal paraffins (CnP) having 20 to25 carbon atoms defined by C20P>C21P>C22P>C23P>C24P>C25P; and

[III] gas oil compositions (C) comprising an FT synthetic base oil in anamount of 60 percent by volume or more on the basis of the total amountof the gas oil composition, with a sulfur content of 5 ppm by mass orless, an aromatic content of 10 percent by volume or less, an oxygencontent of 100 ppm or less, a density of 760 kg/m³ or greater and 840kg/m³ or less, a 90% distillation temperature of 280° C. or higher and350° C. or lower and an end point of 360° C. or lower in distillationcharacteristics, an insoluble content after an oxidation stability testof 0.5 mg/100 mL or less, an HFRR wear scar diameter (WS1.4) of 400 μmor smaller, a cloud point of −3° C. or lower, a cold filter pluggingpoint of −10° C. or lower, a pour point of −12.5° C. or lower, a totalcontent of normal paraffins having 20 to 30 carbon atoms of 4 percent bymass or more and less than 6 percent by mass, a value determined bydividing the total content of normal paraffins having 20 to 30 carbonatoms by the total content of hydrocarbons having 20 to 30 carbon atomsother than the normal paraffins of 0.2 or greater and 0.6 or less, andrelations in the content of each of normal paraffins (CnP) having 20 to25 carbon atoms defined by C20P>C21P>C22P>C23P>C24P>C25P and(C24P-C25P)/C24P>(C22P-C23P)/C22P>(C20P-C21P)/C20P;

(Step 1) a lubricity improver comprising a fatty acid and/or a fattyacid ester is admixed in an amount of 20 mg/L or more and 300 mg/L orless in terms of the active component with the gas oil composition byline-blending, forced-stirring or leaving to stand for a sufficienttime; and

(Step 2) a cold flow improver comprising an ethylene vinyl acetatecopolymer and/or a compound with a surface active effect is admixed inan amount of 20 mg/L or more and 1000 mg/L or less in terms of theactive component with the gas oil composition by line-blending,forced-stirring or leaving to stand for a sufficient time.

Alternatively, the gas oil composition of the present invention ispreferably admixed with 200 mg/L or more and 500 mg/L or less of adetergent comprising a polyether amine compound, a polybutenyl aminecompound, an alkenyl succiniamide compound, or an alkenyl succiniimidecompound by line-blending, forced-stirring or leaving to stand for asufficient time, in a step added between Steps 1 and 2. Preferably, thelubricity improver, detergent and cold flow improver each contain asolvent containing no chemical substance with a melting point of 10° C.or higher. Preferably, the gas oil composition has a peroxide numberafter an accelerated oxidation test of 50 ppm by mass or less, akinematic viscosity at 30° C. of 2.5 mm²/s or greater and 5.0 mm²/s orless, a cetane index of 45 or greater and a water content of 100 ppm byvolume or less.

The sulfur content of the gas oil composition of the present inventionis necessarily 5 ppm by mass or less, preferably 3 ppm by mass or less,more preferably 1 ppm by mass or less, with the objective of reducingpoisonous substances exhausted from an engine and improving exhaust-gaspost-processing system performances. The sulfur content used hereindenotes the mass content of the sulfur components on the basis of thetotal mass of a gas oil composition measured in accordance with JIS K2541 “Crude oil and petroleum products—Determination of sulfur content”.

The aromatic content of the gas oil composition of the present inventionis necessarily 10 percent by volume or less, preferably 8 percent byvolume or less, more preferably 5 percent by volume or less, morepreferably 3 percent by volume or less, most preferably 1 percent byvolume or less. When the composition has an aromatic content of 10percent by volume or less, it can suppress the formation of PM, exhibitenvironment friendly properties and achieve easily and certainlycharacteristics defined in the present invention. The aromatic contentused herein denotes the volume percentage (volume %) of the aromaticcomponent content measured in accordance with JPI-5S-49-97 “PetroleumProducts—Determination of Hydrocarbon Types—High Performance LiquidChromatography” prescribed in JPI Standard and Manuals Testing Methodfor Petroleum Products published by Japan Petroleum Inst.

The oxygen content of the gas oil composition of the present inventionis necessarily 100 ppm by mass or less, preferably 80 ppm by mass orless, more preferably 60 ppm by mass or less, with the objective ofimproving oxidation stability. The oxygen content can be measured with aconventional elemental analysis device. For example, the oxygen contentis measured by converting a sample to CO or further to CO₂ on platinumcarbon and measuring the amount thereof using a thermal conductivitydetector.

The density at 15° C. of the gas oil composition of the presentinvention is preferably 760 kg/m³ or higher, more preferably 765 kg/cm³or higher, and more preferably 770 kg/cm³ or higher with the objectiveof maintaining the calorific value. The density is preferably 840 kg/cm³or lower, more preferably 835 kg/cm³ or lower, and more preferably 830kg/cm³ or lower with the objective of reducing NOx and PM emission. Thedensity used herein denotes the density measured in accordance with JISK 2249 “Crude petroleum and petroleum products—Determination of densityand petroleum measurement tables based on a reference temperature (15°C.)”.

With regard to distillation characteristics, the 90% distillationtemperature of the gas oil composition (A) is necessarily 330° C. orlower. If the 90% distillation temperature is in excess of 330° C.,emission of PM or fine particles would be likely increased. Therefore,the 90% distillation temperature is preferably 327° C. or lower, morepreferably 325° C. or lower. If the 90% distillation temperature is toolow, it would induce deterioration of fuel consumption or reduction ofengine output. Therefore, the lower limit 90% distillation temperatureis necessarily 280° C. or higher, preferably 285° C. or higher, morepreferably 290° C. or higher. For the gas oil compositions (B) and (C),the 90% distillation temperature is necessarily 350° C. or lower. If the90% distillation temperature is in excess of 350° C., emission of PM orfine particles would be likely increased. Therefore, the 90%distillation temperature is preferably 345° C. or lower, more preferably340° C. or lower, more preferably 335° C. or lower. If the 90%distillation temperature is too low, it would induce deterioration offuel consumption or reduction of engine output. Therefore, the lowerlimit 90% distillation temperature is necessarily 280° C. or higher,preferably 285° C. or higher, more preferably 290° C. or higher.

The initial boiling point of the gas oil composition of the presentinvention is necessarily 140° C. or higher. If the initial boiling pointis lower than 140° C., the engine output and high-temperaturestartability would tend to be extremely reduced and deteriorated.Therefore, the initial boiling point is preferably 145° C. or higher,more preferably 150° C. or higher. The end point is preferably 360° C.or lower. If the end point is in excess of 360° C., emission of PM orfine particles would be likely increased. Therefore, the end point ispreferably 368° C. or lower, more preferably 366° C. or lower.

There is no particular restriction on the 10% distillation temperature.However, the lower limit is preferably 160° C. or higher, morepreferably 170° C. or higher, more preferably 180° C. or higher with theobjective of suppressing reduction of engine output and deterioration offuel consumption. The upper limit is preferably 250° C. or lower, morepreferably 245° C. or lower, more preferably 230° C. or lower with theobjective of suppressing deterioration of exhaust gas properties. Theinitial boiling point, 10% distillation temperature, 90% distillationtemperature and end point used herein denote the values measured inaccordance with JIS K 2254 “Petroleum products—Determination ofdistillation characteristics”.

The total insoluble content of the gas oil composition of the presentinvention after an oxidation stability test is necessarily 1.0 mg/100 mLor less, more preferably 0.8 mg/100 mL or less, more preferably 0.5mg/100 mL or less in view or storage stability. The oxidation stabilitytest used herein is carried out at a temperature of 95° C. under oxygenbubbling for 16 hours in accordance with ASTM D2274-94. The totalinsoluble content after an oxidation stability test referred hereindenotes the value measured in accordance with the foregoing oxidationstability test.

The gas oil composition of the present invention have necessarily such alubricity that the HFRR wear scar diameter (WS1.4) is 400 μm or smaller.If the lubricity is too low, the composition would cause a diesel engineequipped with a distribution type injection pump in particular to beincreased in driving torque and in wear on each part of the pump whilethe engine is driven, possibly leading not only to degradation of theexhaust gas properties but also to the breakdown of the engine itself.Also in an electronically controlled fuel injection pump enabling a highpressure injection, wear on the sliding parts would likely occur.Therefore, with respect to the lubricity, the HFRR wear scar diameter(WS1.4) of the gas oil composition is necessarily 400 μm or smaller,preferably 380 μm or smaller, more preferably 360 μm or smaller. Thelubricity, i.e., HFRR wear scar diameter (WS1.4) used herein denotes thelubricity measured in accordance with JPI-5S-50-98 “Gas oil—TestingMethod for Lubricity” prescribed in JPI Standard and Manuals TestingMethod for Petroleum Products published by Japan Petroleum Inst.

With regard to the cloud point of the gas oil composition of the presentinvention, the cloud point of the gas oil composition (A) is necessarily−15° C. or lower, more preferably −16° C. or lower, more preferably −17°C. or lower with the objective of securing low-temperature startabilityand drivability and with the objective of maintaining the injectionperformance of an electronically controlled fuel injection pump. Thecloud point of the gas oil composition (B) is necessarily −5° C. orlower, preferably −6° C. or lower, more preferably −8° C. or lower withthe objective of securing low-temperature startability and drivabilityand with the objective of maintaining the injection performance of anelectronically controlled fuel injection pump. The cloud point of thegas oil composition (C) is necessarily −3° C. or lower, preferably −4°C. or lower, more preferably −5° C. or lower with the objective ofsecuring low-temperature startability and drivability and with theobjective of maintaining the injection performance of an electronicallycontrolled fuel injection pump.

The cloud point used herein denotes the pour point measured inaccordance with JIS K 2269 “Testing Method for Pour Point and CloudPoint of Crude Oil and Petroleum Products”.

With regard to the cold filter plugging point of the gas oil compositionof the present invention, the cold filter plugging point of the gas oilcomposition (A) is necessarily −25° C. or lower. Further, the coldfilter plugging point is preferably −26° C. or lower, more preferably−27° C. or lower with the objective of preventing plugging of thepre-filter of a diesel powered automobile and maintaining the injectionperformance of an electronically controlled fuel injection pump. Thecold filter plugging point of the gas oil composition (B) is necessarily−20° C. or lower. Further, the cold filter plugging point is preferably−21° C. or lower, more preferably −22° C. or lower with the objective ofpreventing plugging of the pre-filter of a diesel powered automobile andmaintaining the injection performance of an electronically controlledfuel injection pump. The cold filter plugging point of the gas oilcomposition (C) is necessarily −10° C. or lower. Further, the coldfilter plugging point is preferably −11° C. or lower, more preferably−12° C. or lower with the objective of preventing plugging of thepre-filter of a diesel powered automobile and maintaining the injectionperformance of an electronically controlled fuel injection pump.

The cold filter plugging point used herein denotes the cold filterplugging point measured in accordance with JIS K 2288 “Gasoil—Determination of cold filter plugging point”.

With regard to the pour point of the gas oil composition of the presentinvention, the pour point of the gas oil composition (A) is necessarily−32.5° C. or lower. Further, the pour point is preferably −35° C. orlower with the objective of securing low-temperature startability ordrivability and maintaining the injection performance of anelectronically controlled fuel injection pump. The pour point of the gasoil composition (B) is necessarily −25° C. or lower. Further, the pourpoint is preferably −22.5° C. or lower with the objective of securinglow-temperature startability or drivability and maintaining theinjection performance of an electronically controlled fuel injectionpump. The pour point of the gas oil composition (C) is necessarily−12.5° C. or lower. Further, the pour point is preferably −15° C. orlower with the objective of securing low-temperature startability ordrivability and maintaining the injection performance of anelectronically controlled fuel injection pump.

The pour point used herein denotes the pour point measured in accordancewith JIS K 2269 “Testing Method for Pour Point and Cloud Point of CrudeOil and Petroleum Products”.

In the present invention, the total content of normal paraffins having20 to 30 carbon atoms in the gas oil composition (A) is necessarily lessthan 2 percent by mass of the total mass of the gas oil composition. Ifthe total content of these heavy normal paraffins is 2 percent by massor more, deposition of wax would be induced at low temperatures.Therefore, the total content is preferably 1.8 percent by mass or less,more preferably 1.6 percent by mass or less. Further, the valuedetermined by dividing the total content of normal paraffins having 20to 30 carbon atoms by the total content of hydrocarbons having 20 to 30carbon atoms other than the normal paraffins is necessarily 0.2 orgreater and 0.6 or less, preferably 0.22 or greater and 0.57 or less,more preferably 0.25 or greater and 0.55 or less in order to improve theadditive solubility of the gas oil base oil. If the value is less than0.2, the additive solubility would be extremely reduced. If the value isgreater than 0.6, the cold flowability would be impaired. Further, thecontent of each of normal paraffins (CnP) within the carbon number (n)range from 15 to 20 necessarily satisfies the relation defined byC20P<C19P<C18P<C17P<C16P<C15P. As long as this relation is satisfied,the resulting composition will have a stable wax deposition ratecorrespondingly to temperature changes such as the out door temperatureat which the composition is cooled and be able to ensure the cold flowimprover to exhibit its properties stably due to the effects of thenormal paraffins present in the aforesaid content.

The total content of the straight-chain saturated hydrocarbons having 20to 30 carbon atoms and content of the straight-chain saturatedhydrocarbons having 15 to 20 carbon atoms are the values measured usingGC-FID wherein the column is a capillary column formed of methylsilicone (ULTRA ALLOY-1), the carrier gas is helium and the detector isa flame ionization detector (FID), under conditions wherein the columnlength is 30 m, the carrier gas flow rate is 1.0 mL/min, the ratio ofdivision is 1:79, the sample injection temperature is 360° C., thecolumn is heated up from 140° C. to 355° C. (8° C./min), and thedetector temperature is 360° C.

For the gas oil composition (B), the total content of normal paraffinshaving 20 to 30 carbon atoms thereof is necessarily 2 percent by mass ormore and less than 4 percent by mass of the total mass of the gas oilcomposition. If the total content of these heavy normal paraffins is 4percent by mass or more, deposition of wax would be induced at lowtemperatures. If the total content is less than 2 percent by mass, theamount of the heavy normal paraffins would be reduced, resulting in areduction in the performance efficiency of the cold flow improver, whichutilizes the heavy paraffins as a growth core. Further, the valuedetermined by dividing the total content of normal paraffins having 20to 30 carbon atoms by the total content of hydrocarbons having 20 to 30carbon atoms other than the normal paraffins is necessarily 0.2 orgreater and 0.6 or less, preferably 0.22 or greater and 0.57 or less,more preferably 0.25 or greater and 0.55 or less in order to improve theadditives solubility of the gas oil base oil. If the value is less than0.2, the additive solubility of would be extremely reduced. If the valueis greater than 0.6, the cold flowability would be impaired. Further,the content of each of normal paraffins (CnP) within the carbon number(n) range from 20 to 25 necessarily satisfies the relation defined byC20P>C21P>C22P>C23P>C24P>C25P. As long as this relation is satisfied,the resulting composition will have a stable wax deposition ratecorrespondingly to temperature changes such as the out door temperatureat which the composition is cooled and be able to ensure the cold flowimprover to exhibit its properties stably due to the effects of thenormal paraffins present in the aforesaid content.

The total content of the straight-chain hydrocarbons having 20 to 30carbon atoms and content of the straight-chain saturated hydrocarbonshaving 20 to 25 carbon atoms are the values measured using GC-FIDwherein the column is a capillary column formed of methyl silicone(ULTRA ALLOY-1), the carrier gas is helium and the detector is a flameionization detector (FID), under conditions wherein the column length is30 m, the carrier gas flow rate is 1.0 mL/min, the ratio of division is1:79, the sample injection temperature is 360° C., the column is heatedup from 140° C. to 355° C. (8° C./min), and the detector temperature is360° C.

For the gas oil composition (C), the total content of normal paraffinshaving 20 to 30 carbon atoms thereof is necessarily 4 percent by mass ormore and less than 6 percent by mass of the total mass of the gas oilcomposition. If the total content of these heavy normal paraffins is 6percent by mass or more, deposition of wax would be induced at lowtemperatures. If the total content is less than 4 percent by mass, theamount of the heavy normal paraffins would be reduced, resulting in areduction in the performance efficiency of the cold flow improver, whichutilizes the heavy paraffins as a growth core. Further, the valuedetermined by dividing the total content of normal paraffins having 20to 30 carbon atoms by the total content of hydrocarbons having 20 to 30carbon atoms other than the normal paraffins is necessarily 0.2 orgreater and 0.6 or less, preferably 0.22 or greater and 0.57 or less,more preferably 0.25 or greater and 0.55 or less in order to improve theadditive solubility of the gas oil base oil. If the value is less than0.2, the additive solubility would be extremely reduced. If the value isgreater than 0.6, the cold flowability would be impaired. Further, thecontent of each of normal paraffins (CnP) within the carbon number (n)range from 20 to 25 necessarily satisfies the relation defined byC20P>C21P>C22P>C23P>C24P>C25P and also the relation defined by(C24P-C25P)/C24P>(C22P-C23P)/C22P>(C20P-C21P)/C20P.

Herein, “(C24P-C25P)/C24P>(C22P-C23P)” is the value determined bydividing the content of normal paraffins having 24 and 25 carbon atomsby the content of a normal paraffin having 24 carbon atoms. Also,“(C22P-C23P)/C22P>(C20P-C21P)/C20P” is calculated in the same manner.These relations were obtained as the results of extensive research andstudy by the inventor of the present invention. What is meant by therelations is to express the deposition rate of the heavy normalparaffins with respect to temperature in a simple manner. As long asthese relations are satisfied, the resulting composition will have astable wax deposition rate correspondingly to temperature changes suchas the out door temperature at which the composition is cooled and beable to ensure the cold flow improver to exhibit its properties stably,due to the effects of the normal paraffins present in the aforesaidcontent.

The total content of the straight-chain saturated hydrocarbons having 20to 30 carbon atoms and content of the straight-chain saturatedhydrocarbon having 20 to 25 carbon atoms are the values measured usingGC-FID wherein the column is a capillary column formed of methylsilicone (ULTRA ALLOY-1), the carrier gas is helium and the detector isa flame ionization detector (FID), under conditions wherein the columnlength is 30 m, the carrier gas flow rate is 1.0 mL/min, the ratio ofdivision is 1:79, the sample injection temperature is 360° C., thecolumn is heated up from 140° C. to 355° C. (8° C./min), and thedetector temperature is 360° C.

The peroxide number of the gas oil composition of the present inventionafter an accelerated oxidation test (oxidation stability test) ispreferably 50 ppm by mass or less, more preferably 40 ppm by mass orless, 30 ppm by mass or less in view of storage stability andcompatibility to parts. The peroxide number after an acceleratedoxidation test used herein denotes the value measured in accordance withJPI-5S-46-96 prescribed in JPI Standard after an accelerated oxidationtest is carried out at a temperature of 95° C. under oxygen bubbling for16 hours in accordance with ASTM D2274-94. If necessary, the gas oilcompositions of the present invention may be blended with additives suchas anti-oxidants or metal deactivators in order to reduce the peroxidenumber.

The kinematic viscosity at 30° C. of the gas oil composition of thepresent invention is preferably 2.5 mm²/s or higher, more preferably2.55 mm²/s or higher, more preferably 2.6 mm²/s or higher. If thekinematic viscosity is lower than 2.5 mm²/s, it would be difficult tocontrol the fuel injection timing at the fuel injection pump side, andlubricity at each part of the fuel injection pump installed in an enginewould be reduced. There is no particular restriction on the upper limitkinematic viscosity at 30° C. However, the kinematic viscosity ispreferably 5.0 mm²/s or lower, more preferably 4.8 mm²/s or lower, morepreferably 4.5 mm²/s or lower with the objective of suppressing increaseof the NOx and PM concentrations in the exhaust gas, caused bydestabilization of the fuel injection system due to an increase inresistance therein. The kinematic viscosity used herein denotes thevalue measured in accordance with JIS K 2283 “Crude petroleum andpetroleum products—Determination of kinematic viscosity and calculationof viscosity index from kinematic viscosity”.

The cetane index of the gas oil composition of the present invention ispreferably 45 or greater. If the cetane index is lower than 45, theconcentrations of PM, aldehydes, and NOx in exhaust gas would likely beincreased. For the same reason, the cetane index is more preferably 47or greater, more preferably 50 or greater. There is no particularrestriction on the upper limit of the cetane index. However, if thecetane index is greater than 80, discharge of soot would likely beincreased during the acceleration of a vehicle. Therefore, the cetaneindex is preferably 78 or lower, more preferably 75 or lower, morepreferably 73 or lower. The cetane index used herein denotes the valuecalculated in accordance with “8.4 cetane index calculation method usingvariables equation” prescribed in JIS K 2280 “Petroleumproducts—Fuels—Determination of octane number, cetane number andcalculation of cetane index”. The cetane index defined by the JISstandards is generally applied to gas oil containing no cetane numberimprover. However, in the present invention, “8.4 cetane indexcalculation method using variables equation” is applied to a gas oilcontaining a cetane number improver, and the value obtained thereby isalso defined as cetane index.

There is no particular restriction on the cetane number of the gas oilcompositions of the present invention as long as the above-describedcharacteristics are satisfactorily obtained. However, the cetane numberis preferably 45 or greater, more preferably 47 or greater, morepreferably 50 or greater with the objective of inhibiting knockingduring diesel combustion and reducing the discharge of NOx, PM andaledhydes in the exhaust gas. With the objective of reducing black smokein the exhaust gas, the cetane number is preferably 80 or lower, morepreferably 78 or lower, more preferably 75 or lower. The cetane numberused herein denotes the cetane number measured in accordance with “7.Cetane number test method” prescribed in JIS K 2280 “Petroleumproducts—Fuels—Determination of octane number, cetane number andcalculation of cetane index”.

The water content of the gas oil composition of the present invention ispreferably 100 ppm by volume, more preferably 50 ppm by volume, morepreferably 20 ppm by volume with the objective of preventing thecompositions from freezing and the engine interior from corroding. Thewater content used herein denotes the value measured in accordance withJIS K 2275 “Crude oil and petroleum products—Determination of watercontent—Potentiometric Karl Fischer titration method”.

The flash point of the gas oil composition of the present invention ispreferably 45° C. or higher. A flash point of lower than 45° C. is notpreferable in view of safety. Therefore, the flash point is preferably47° C. or higher, more preferably 50° C. or higher. The flash point usedherein denotes the value measured in accordance with JIS K 2265 “Crudeoil and petroleum products—Determination of flash point”.

There is no particular restriction on the carbon residue of the 10%distillation residue of the gas oil composition of the presentinvention. However, the carbon residue of the 10% distillation residueis preferably 0.1 percent by mass or less, more preferably 0.08 percentby mass or less, more preferably 0.05 percent by mass or less with theobjective of reducing fine particles and PM, maintaining theperformances of the exhaust-gas post-processing system installed in anengine and preventing sludge from plugging a filter.

The carbon residue of the 10% distillation residue used herein denotesthat measured in accordance with JIS K 2270 “Crude petroleum andpetroleum products—Determination of carbon residue”.

In the present invention, it is necessary that the gas oil compositionis first admixed with a lubricity improver by line-blending,forced-stirring or leaving to stand for a sufficient time (Step 1) andthen admixed with a cold flow improver by line-blending, forced-stirringor leaving to stand for a sufficient time (Step 2). Alternatively,depending on properties required for fuel, between Steps 1 and 2 may beprovided a step wherein a detergent is admixed with the gas oilcomposition by line-blending, forced-stirring or leaving to stand for asufficient time. Further, according to the situations, other additivessuch as cetane number improvers may be blended in a suitable amount.

The line-blending referred to as a method of mixing the gas oilcomposition with additives denotes a method wherein the additives areadded to the gas oil composition on the pathway of transfer thereofunder pressure between, for example, a storage tank and a storage tank,a production unit and a production unit or a production unit and astorage tank to be diffused and mixed until the composition passes fromthe upstream to the downstream. The forced-stirring denotes a methodwherein while the gas oil composition is present in a storage tank or aproduction unit, the additives are added thereto and forcedly diffusedand mixed by forced circulation with a pump and stirring with a stirrer.The leaving to stand denotes a method wherein the gas oil composition towhich the additives are added by any of various methods or in a storagetank or a production unit is left to stand there for a sufficient periodto be diffused and mixed through natural diffusion and naturalconvection. In any of the mixing methods, the gas oil may be heated soas to improves the mixing efficiency.

With regard to Steps 1 and 2, there is no particular restriction thereonas long as the gas oil composition of the present invention can beprepared by complying with the order of adding the additives and themethod of mixing the gas oil composition and the additives. Therefore,there may be used any adding method used for producing a gas oilcomposition in a refinery. With regard to a method of adding a cold flowimprover, a method has been used frequently wherein it is added to a gasoil to be produced after diluted with a solvent, kerosene or gas oil orwherein it is added after heated at a temperature which is 10° C. higherthan the environment temperature.

Preferably, the additives used in the present invention contain nosolvent containing a chemical substance the melting point of which is10° C. or higher. If a solvent with a melting point of 10° C. or higheris used, the solvent would deposit earlier than the wax of the gas oil,resulting in deterioration of the low-temperature properties thereof.Examples of solvents with a melting point of 10° C. or higher includesaturated alcohols wherein hydroxyl groups bond to a straight-chainalkyl group having 11 or more carbon atoms and the terminal groups (forexample, dodecyl alcohol) and compounds having a phenol group. With theobjective of reducing load to the environment, it is preferable not touse so-called endocrine disrupter or substances, the use of which areprohibited from the view of the environment protection, in theseadditives or solvents therefore.

It is necessary to add a lubricity improver to the gas oil compositionof the present invention. With the objective of preventing a fuelinjection pump from wearing, the amount of the lubricity improver isnecessarily 20 mg/L or more and 300 mg/L or less, preferably 50 mg/L ormore and 200 mg/L or less, in terms of the concentration of the activecomponent. When the lubricity improver is blended in an amount withinthese ranges, the lubricity improver can effectively exhibit itsefficacy. For example, in a diesel engine equipped with a distributiontype injection pump, the lubricity improver can suppress the drivingtorque from increasing and can reduce wear on each part of the pumpwhile the engine is driven.

The lubricity improvers must be those of type containing a compound witha polar group, comprising a fatty acid and/or a fatty acid ester. Thereis no particular restriction on the specific name of the compound. Thelubricity improver may, therefore, be any one or more type selected fromcarboxylic acid-, ester-, alcohol- and phenol-based lubricity improvers.Among these lubricity improvers, preferred are carboxylic acid- andester-based lubricity improvers. The carboxylic acid-based lubricityimprover may be linoleic acid, oleic acid, salicylic acid, palmiticacid, myristic acid or hexadecenoic acid or a mixture of two or more ofthese carboxylic acids. Examples of the ester-based lubricity improverinclude carboxylic acid esters of glycerin. The carboxylic acid formingthe carboxylic acid ester may be of one or more types. Specific examplesof the carboxylic acid include linoleic acid, oleic acid, salicylicacid, palmitic acid, myristic acid or hexadecenoic acid. The averagemolecular weight of the active component of the lubricity improver ispreferably 200 or greater and 1000 or less in order to enhance thesolubility to the gas oil composition.

To the gas oil composition of the present invention must be added a coldflow improver through a predetermined step with the objective ofpreventing the filter of a diesel powered automobile from plugging. Theamount of the cold flow improver is necessarily 20 mg/L or more and 1000mg/L or less, preferably 300 mg/L or more and 800 mg/L or less in termsof the active component concentration.

The cold flow improver must be an ethylene-vinyl acetate copolymerand/or a compound with a surface active effect. Examples of the coldflow improver having a surface active effect include one or more typesselected from copolymers of ethylene and methyl methacrylate, copolymersof ethylene and a-olefin, chlorinated methylene-vinyl acetatecopolymers, alkyl ester copolymers of unsaturated carboxylic acids,eaters synthesized from nitrogen-containing compounds having a hydroxylgroup and saturated fatty acids and salts of the esters, esters andamide derivatives synthesized from polyhydric alcohols and saturatedfatty acids, esters synthesized from polyoxyalkylene glycol andsaturated fatty acid, esters synthesized from alkyleneoxide adducts ofpolyhydric alcohols or partial esters thereof and saturated fatty acids,chlorinated paraffin/naphthalene condensates, alkenyl succiniamides, andamine salts of sulfobenzoic acids.

Other than the above-exemplified cold flow improvers, the gas oilcomposition of the present invention may contain any one or more typeselected from alkenyl succinamides; linear compounds such as dibehenicacid esters of polyethylene glycols; polar nitrogen compounds composedof reaction products of acids such as phthalic acid,ethylenediaminetetraacetic acid and nitriloacetic acid or acid anhydridethereof and hydrocarbyl-substituted amines; and comb polymers composedof alkyl fumarates- or alkyl itaconates-unsaturated ester copolymers.

Since commercially available products referred to as cold flow improversare often in the form in which the active components contributing tolow-temperature fluidity (active components) are diluted with a suitablesolvent. Therefore, the above amount of the cold flow improvers denotesthe amount of the active components (active component concentration)when such commercially available products are added to the gas oilcomposition of the present invention.

To the gas oil composition of the present invention may be added adetergent if necessary. However, it is necessary that the detergent isadded after addition of the lubricity improver and before addition ofthe cold flow improver, or simultaneously with addition of the lubricityimprover. There is no particular restriction on the components of thedetergent. Examples of the detergents include ashless dispersants, forexample, polyether amine compounds which are reactions products ofbutyleneoxide and amine; polybutenyl amine compounds which are reactionproducts of isobutylene copolymers and amine; imide compounds; alkenylsuccinimides such as polybutenyl succinimide synthesized frompolybutenyl succinic anhydrate and ethylene polyamines; succinic acidesters such as polybutenyl succinic acid ester synthesized frompolyhydric alcohols such as pentaerythritol and polybutenyl succinicanhydrate; copolymerized polymers such as copolymers ofdialkylaminoethyl methacrylates, polyethylene glycol methacrylates, orvinylpyrrolidon and alkylmethacrylates; and reaction products ofcarboxylic acids and amines. Among these, preferred are alkenylsuccinimides and reaction products of carboxylic acids and amines. Thesedetergents may be used alone or in combination. When an alkenylsuccinimide is used, an alkenyl succinimide having a molecular weight of1000 to 3000 may be used alone, or an alkenyl succinimide having amolecular weight of 700 to 2000 and an alkenyl succinimide having amolecular weight of 10000 to 20000 may be used in combination.Carboxylic acids constituting reaction products of carboxylic acids andamines may be of one or more types. Specific examples of the carboxylicacids include fatty acids having 12 to 24 carbon atoms and aromaticcarboxylic acids having 7 to 24 carbon atoms. Examples of fatty acidshaving 12 to 24 carbon atoms include, but not limited thereto, linoleicacid, oleic acid, palmitic acid, and myristic acid. Examples of aromaticcarboxylic acids having 7 to 24 carbon atoms include, but not limitedthereto, benzoic acid and salicylic acid. Amines constituting reactionproducts of carboxylic acids and amines may be of one or more types.Typical examples of amines used herein include, but not limited thereto,oleic amines. Various amines may also be used.

There is no particular restriction on the amount of the detergent to beblended. However, the amount is preferably 20 mg/L or more, morepreferably 50 mg/L or more, and more preferably 100 mg/L or more, on thebasis of the total mass of the composition, because the detergent canperform its effect to suppress a fuel injection nozzle from plugging.The effect may not be obtained if the amount is less than 20 mg/L. Onthe other hand, if the detergent is blended in a too much amount, itseffect as balanced with the amount is not obtained. Therefore, theamount of the detergent is preferably 500 mg/L or less, more preferably300 mg/L or less, more preferably 200 mg/L or less because the detergentmay increase the amounts of NOx, PM and aldehydes in the exhaust gasfrom a diesel engine. Commercial available detergents are generallyavailable in a state wherein the active component contributing todetergency is diluted with a suitable solvent. In the case where suchproducts are blended with the gas oil compositions of the presentinvention, the content of the active component is preferably within theabove-described range.

If necessary, the gas oil compositions of the present invention may beblended with a cetane number improver in a suitable amount to enhancethe cetane number of the composition.

The cetane number improver may be any of various compounds known ascetane number improvers for gas oil. Examples of such cetane numberimprovers include nitrate esters and organic peroxides. These cetanenumber improvers may be used alone or in combination. Preferred for usein the present invention are nitrate esters. Examples of the nitrateesters include various nitrates such as 2-chloroethyl nitrate,2-ethoxyethyl nitrate, isopropyl nitrate, butyl nitrate, primary amylnitrate, secondary amyl nitrate, isoamyl nitrate, primary hexyl nitrate,secondary hexyl nitrate, n-heptyl nitrate, n-octyl nitrate, 2-ethylhexylnitrate, cyclohexyl nitrate, and ethylene glycol dinitrate. Particularlypreferred are alkyl nitrates having 6 to 8 carbon atoms.

The content of the cetane number improver is preferably 500 mg/L ormore, more preferably 600 mg/L or more, more preferably 700 mg/L ormore, more preferably 800 mg/L or more, most preferably 900 mg/L ormore. If the content of the cetane number improver is less than 500mg/L, the cetane number improving effect may not be attainedsufficiently, leading to a tendency that PM, aldehydes, and NOx in theexhaust gas from a diesel engine are not reduced sufficiently. There isno particular restriction on the upper limit content of the cetanenumber improver. However, the upper limit is preferably 1400 mg/L orless, more preferably 1250 mg/L or less, more preferably 1100 mg/L orless, and most preferably 1000 mg/L or less, on the basis of the totalmass of the gas oil composition.

The cetane number improver may be any of those synthesized in accordancewith conventional methods or commercially available products. Suchproducts in the name of cetane number improver are available in a statewherein the active component contributing to an improvement in cetanenumber (i.e., cetane number improver itself) is diluted with a suitablesolvent. In the case where the gas oil composition of the presentinvention is prepared using any of such commercially available products,the content of the effective component is preferably within theabove-described range.

In order to further enhance the properties of the gas oil compositionsof the present invention, other known fuel oil additives (hereinafterreferred to as “other additives” for convenience) may be used alone orin combination. Examples of the other additives include phenolic- andaminic anti-oxidants; metal deactivators such as salicylidenderivatives; anti-corrosion agents such as aliphatic amines and alkenylsuccinic acid esters; anti-static additives such as anionic, cationic,and amphoteric surface active agents; coloring agents such as azo dye;silicone-based defoaming agents and anti-icing agents such as2-methoxyethanol, isopropyl alcohol and polyglycol ethers.

The amounts of the other additives may be arbitrarily selected. However,the amount of each of the other additives is preferably 0.5 percent bymass or less, more preferably 0.2 percent by mass or less, on the basisof the total mass of the composition.

There is no particular restriction on the other specification of adiesel engine where the gas oil composition of the present invention isused, the applications thereof, the environment where the gas oilcomposition is used.

As described above, according to the present invention, the use of a gasoil composition produced by the above-described process to satisfyrequirements regarding fraction and the like renders it possible toproduce easily a gas oil composition suitable for a winter season thatcan achieve environment load reduction, low-temperature properties andlow fuel consumption all together, which have been difficult to achievewith the conventional gas oil compositions even though the gas oilcomposition of the present invention contains mainly an FT syntheticbase oil.

[Applicability in the Industry]

The present invention can provide a gas oil composition suitable for awinter season that can achieve environment load reduction,low-temperature performance and low fuel consumption all together.

EXAMPLES

Hereinafter, the present invention will be described in more detail byway of the following examples and comparative examples, which should notbe construed as limiting the scope of the invention.

The characteristics of gas oil compositions were measured by thefollowing methods. The component ratio of each fraction and cetanenumber thereof were measured after base oils were blended and distilled.

The density referred herein denotes the density measured in accordancewith JIS K 2249 “Crude petroleum and petroleum products—Determination ofdensity and petroleum measurement tables based on a referencetemperature (15° C.)”.

The kinematic viscosity referred herein denotes the viscosity measuredin accordance with JIS K 2283 “Crude petroleum and petroleumproducts—Determination of kinematic viscosity and calculation ofviscosity index from kinematic viscosity”.

The flash point referred herein denotes the value measured in accordancewith JIS K 2265 “Crude oil and petroleum products—Determination of flashpoint”.

The sulfur content referred herein denotes the mass content of thesulfur components on the basis of the total mass of the composition,measured in accordance with JIS K 2541 “Crude oil and petroleumproducts—Determination of sulfur content”.

The oxygen content referred herein denotes the value measured with athermal conductivity detector after the samples were converted to CO oralternatively further to CO₂, on platinum carbon.

All of the distillation characteristics referred herein denotes thevalues measured in accordance with JIS K 2254 “Petroleumproducts—Determination of distillation characteristics”.

The content of normal paraffins every carbon number (hereinafter refrredto as “CnP”), content of normal paraffins having 20 to 30 carbon atoms(hereinafter referred to as “C20-C30P”) and content of hydrocarbonshaving 20 to 30 carbon atoms other than the normal paraffins having 20to 30 carbon atoms (hereinafter referred to as “C20-C30 hydrocarboncontent other than C20-C30P”) and the value determined by dividing thetotal content of normal paraffins having 20 to 30 carbon atoms by thetotal content of hydrocarbons having 20 to 30 carbon atoms other thanthe normal paraffins having 20 to 30 carbon atoms (C20-C30P/C20-C30hydrocarbon content other than C20-C30P) are the values (mass %)measured with GC-FID or the values calculated therefrom, that is, thosemeasured under conditions wherein the column is a capillary columnformed of methyl silicone (ULTRA ALLOY-1), the carrier gas is helium andthe detector is a flame ionization detector (FID), under conditionswherein the column length is 30 m, the carrier gas flow rate is 1.0mL/min, the ratio of division is 1:79, the sample injection temperatureis 360° C., the column is heated up from 140° C. to 355° C. (8° C./min),and the detector temperature is 360° C.

The cetane index and cetane number referred herein denote the valuescalculated in accordance with “8.4 cetane number calculation methodusing variables equation” prescribed in JIS K 2280 “Petroleumproducts—Fuels—Determination of octane number, cetane number andcalculation of cetane number”.

The cloud point referred herein denotes that measured in accordance withJIS K 2269 “Testing Method for Pour Point and Cloud Point of Crude Oiland Petroleum Products”.

The cold filter plugging point referred herein denotes that measured inaccordance with JIS K 2288 “Gas oil—Determination of cold filterplugging point”.

The pour point referred herein denotes that measured in accordance withJIS K 2269 “Testing Method for Pour Point and Cloud Point of Crude Oiland Petroleum Products”.

The carbon residue content of the 10% distillation residue referredherein denotes that measured in accordance with JIS K 2270 “Crudepetroleum and petroleum products—Determination of carbon residue”.

The aromatic content referred herein denotes the volume percentage(volume %) of the aromatic component content measured in accordance withJPI-5S-49-97 “Petroleum Products—Determination of Hydrocarbon Types—HighPerformance Liquid Chromatography” prescribed in JPI Standard andManuals Testing Method for Petroleum Products published by JapanPetroleum Inst.

The peroxide number after an oxidation stability test referred hereindenotes the value measured in accordance with JPI-5S-46-96 prescribed inJPI Standard and Manuals Testing Method for Petroleum Products publishedby Japan Petroleum Inst after the compositions are subjected to anaccelerated oxidation at a temperature of 95° C. under oxygen bubblingfor 16 hours in accordance with ASTM D2274-94.

The insoluble content after an oxidation stability test referred hereindenotes the value measured after the compositions are subjected to anaccelerated oxidation at a temperature of 95° C. under oxygen bubblingfor 16 hours in accordance with ASTM D2274-94.

The lubricity, i.e., HFRR wear scar diameter (WS1.4) referred hereindenotes lubricity measured in accordance with JPI-5S-50-98 “Gasoil—Testing Method for Lubricity” prescribed in JPI Standard and ManualsTesting Method for Petroleum Products published by Japan Petroleum Inst.

The water content referred herein denotes that measured in accordancewith JIS K 2275 “Crude oil and petroleum products—Determination of watercontent—Potentiometric Karl Fischer titration method”.

Examples 1 and 2, and Comparative Example 1

Base oils with characteristics set forth in Table 1 were blended toproduce gas oil compositions set forth in Table 2 (Examples 1 and 2 andComparative Example 1). FT synthetic base oils 1 and 2 are hydrocarbonmixtures produced by converting natural gas to wax or a middle fractionthrough FT reaction, followed by hydrotreating. The reaction conditionsfor each FT synthetic base oil varied. FT synthetic base oil 1 is a baseoil produced by isomerization positively carried out. FT synthetic baseoil 2 is a base oil resulting from a treatment wherein too much emphasiswas not placed on isomerization. The highly hydrotreated base oil is ahydrocarbon base oil produced by further hydrotreating a gas oil baseoil to further reduce the sulfur and aromatic contents. The processedoil derived from an animal or vegetable oil is an oil produced byhydrotreating palm oil (whole component) used as the raw material toremove the foreign substance. The hydrorefined gas oil corresponds to acommercially available JIS No. 2 gas oil which is used in a winterseason. The gas oil compositions of Examples 1 and 2 and ComparativeExample 1 were produced by blending these base oils in suitable amountsor using any of the base oils as the whole.

The additives used in these examples are as follows:

-   -   Lubricity improver: Infineum R 655 manufactured by Infineum        Japan Ltd. (active component: straight-chain alkylester mixture        containing a fatty acid as the raw material, average molecular        weight: 250 MW)    -   Detergent: alkenyl succinimide mixture    -   Cold flow improver: Infineum R240 manufactured by Infineum Japan        Ltd. (active component: ethylene-vinyl acetate copolymer        mixture, solvent: alkylbenzene) (melting point: −50° C. or        lower)

In Example 1, additives were added through predetermined steps, i.e.,steps wherein the lubricity improver was added and then sufficientlymixed and forced-stirred, and the cold flow improver was added and thensufficiently mixed and forced-stirred. Also in Example 2, additives wereadded through predetermined steps, i.e., steps wherein the lubricityimprover and the detergent were added and then sufficiently mixed andforced-stirred, and the cold flow improver was added and thensufficiently mixed and forced-stirred. In Comparative Example 1, onlythe cold flow improver was added. It was confirmed that these additivesused in these examples contained no solvent with a boiling point of 10°C. or higher.

Table 2 sets forth the blend ratio of the gas oil compositions thusprepared and the 15° C. density, 30° C. kinematic viscosity, flashpoint, sulfur content, oxygen content, distillation characteristics,content of normal paraffins every carbon number (CnP), content of normalparaffins having 20 to 30 carbon atoms (C20-C30P), value determined bydividing the total content of normal paraffins having 20 to 30 carbonatoms by the total content of hydrocarbons having 20 to 30 carbon atomsother than the normal paraffins, cetane index, cetane number, aromaticcontent, cloud point, cold filter plugging point, pour point, carbonresidue content of the 10% distillation residue, insoluble content andperoxide number after an oxidation stability test, wear scar diameterand water content of each composition.

The gas oil composition used in Examples 1 and 2 were produced byblending 60 percent by mass or more of the FT synthetic base oils as setforth in Table 2. Further, as apparent from Table 2, gas oilcompositions satisfying the characteristics as defined herein wereeasily produced without fail, in Examples 1 and 2 wherein the FTsynthetic base oils were blended within the range defined herein. On theother hand, as apparent from Comparative Example 1, where thecomposition did not have the characteristics prescribed in the presentinvention or was not admixed with the predetermined additives as definedin Steps 1 and 2 of the present invention, the gas oil composition asintended by the present invention was not produced.

Next, the following various tests were carried out using the gas oilcompositions of Examples 1 and 2 and Comparative Example 1. All resultsare set forth in Table 3. As apparent from Table 3, the gas oilcompositions of Examples 1 and 2 are those with environment loadreducing properties, which are excellent in fuel consumption propertiesand low-temperature startability, compared with the gas oil compositionof Comparative Example 1 and thus are high quality fuels that canachieve at a high level excellent fuel consumption properties andlow-temperature startability in a winter season, that were difficult toachieve with the conventional gas oil compositions.

(Diesel Combustion Test)

A vehicle 1 was driven using each gas oil composition under a test modeshown in FIG. 1 to measure NOx, smoke and fuel consumption. The resultsobtained using the fuel in Comparative Example 1 were defined as 100,and the results of the other fuels were relatively evaluated bycomparison with the results of Comparative Example 1 (smaller valuesindicate better results).

(Low-Temperature Startability Test)

Using the vehicle 1 and on a chassis dynamometer capable of controllingthe environment temperature, each of the gas oil compositions wassubjected to a test carried out at room temperature by (1) flashing(washing) the fuel system of a test diesel vehicle with a fuel to beevaluated; (2) draining out the flashing fuel; (3) replacing the mainfilter with new one; and (4) feeding the fuel tank with the fuel to beevaluated in a specific amount (½ of the tank volume of the testvehicle). The test was continued by (5) cooling rapidly the environmenttemperature from room temperature to −15° C.; (6) keeping thetemperature at −15° C. for one hour; (7) cooling gradually at a rate of1° C./h till reaching to the predetermined temperature (−25° C.); and(8) starting the engine after the temperature was kept at thepredetermined temperature for one hour. If the engine did not start evenafter 10 second cranking was repeated twice at an interval of 30seconds, the fuel was evaluated as “Not passed” at this moment. If theengine started while 10 second cranking was repeated twice at aninterval of 30 seconds, it was idled for 3 minutes and then the vehiclewas speeded up to 60 km/h over 15 seconds and driven at the low speed.When defects in operation (hunting, stumble, vehicle speed reduction orengine stop) were observed while the vehicle was speeded up to 60 km/hand driven at that speed for 20 minutes, the gas oil composition wasevaluated as “Not passed” at this moment. If the engine ran until theend without any defect, the gas oil composition was evaluated as“Passed”.

(Vehicle specification): Vehicle 1

-   -   Type of engine: in-line 4 cylinder intercooled supercharged        diesel engine with EGR    -   Displacement: 1.4 L    -   Internal diameter×stroke: 73 mm×81.4 mm    -   Compression ratio: 18.5 (altered to 16.0)    -   Maximum output: 72 kW/4000 rpm    -   Adopted regulation: 2002 Exhaust Gas Emission Regulation    -   Vehicle weight: 1060 kg    -   Transmission: 5-speed manual transmission    -   Exhaust-gas post-processing device: oxidation catalyst

TABLE 1 Processed oil derived Highly from FT hydrogenated animal or FTsynthetic synthetic processed vegetable Hydrorefined base oil 1 base oil2 oil oil gas oil Density (15° C.) kg/m³ 778 771 814 765 831 Kinematicviscosity (30°) mm²/s 3.0 2.8 3.4 2.3 4.4 Distillation 10% distillation195.0 217.0 217.5 226.5 230.0 characteristics ° C. temperature 50%distillation 243.5 264.0 272.0 249.5 292.5 temperature 90% distillation323.5 324.5 322.5 267.0 345.0 temperature Sulfur content mass % <1 <1 <1<1 8

TABLE 2 Example Example Comparative 1 2 Example 1 FT synthetic base oil1 100 60 FT synthetic base oil 2 100 Highly hydrogenated processed oil10 Processed oil derived from animal or vegetable oil 10 Hydrorefinedgas oil 20 Density (15° C.) kg/m³ 778 790 771 Kinematic viscosity (30°C.) mm²/s 3.0 3.2 2.8 Flash point ° C. 58 62 58 Sulfur content mass ppm<1 <1 <1 Oxygen content mass ppm <10 <10 120 Distillation Initialboiling point 158.5 161.0 171.0 characteristics ° C. 10% distillationtemperature 195.0 202.0 217.0 50% distillation temperature 243.5 254.0264.0 90% distillation temperature 323.5 324.0 324.5 End point 359.0355.5 369.0 CnP C15 2.5 2.3 3.2 mass % C16 2.3 2.1 3.4 C17 1.9 1.8 3.1C18 1.8 1.4 2.6 C19 1.5 1.1 2.6 C20 1.1 0.7 1.9 C20-C30P 1.8 1.5 2.4C20-30 hydrocarbon content mass % 7.5 4.4 12.6 other than C20-30PC20-C30P/C20-C30 hydrocarbon content other than C20-30P 0.24 0.34 0.19Cetane index 72.0 69.6 85.7 Cetane number 65.5 64.0 80.9 Aromaticcontent vol. % <1 3.6 <1 Cloud point ° C. −17.0 −19.0 −13.0 Cold filterplugging point ° C. −28.0 −29.0 −17.0 Pour point ° C. −35.0 −37.5 −22.5Carbon residue content of mass % 0.00 0.00 0.00 10% distillation residuePeroxide number mass ppm 0 15 1 Wear scar diameter (WS 1.4) μm 360 340460 Insoluble content mg/100 mL 0.1 0.1 0.7 Water content vol. ppm 19 247 Lubricity improver mg/L 150 150 — Detergent mg/L — 100 — Cold flowimprover mg/L 300 300 300 Cetane number improver mg/L — — —

TABLE 3 Example Example Comparative 1 2 Example 1 Fuel consumption 89 86100 properties Vehicle exhaust gas NOx 96 98 100 Smoke 94 96 100Low-temperature −25° C. Passed Passed Not Passed startability test

Example 3 and 4, and Comparative Example 2

Base oils with characteristics set forth in Table 4 were blended toproduce gas oil compositions set forth in Table 5 (Examples 3 and 4 andComparative Example 2). FT synthetic base oils 3 and 4 are hydrocarbonmixtures produced by converting natural gas to wax or a middle fractionthrough FT reaction, followed by hydrotreating. The reaction conditionsfor each FT synthetic base oil varied. FT synthetic base oil 3 is a baseoil produced by isomerization positively carried out. FT synthetic baseoil 4 is a base oil resulting from a treatment wherein too much emphasiswas not placed on isomerization. The highly hydrotreated base oil is ahydrocarbon base oil produced by further hydrotreating a gas oil baseoil to further reduce the sulfur and aromatic contents. The processedoil derived from an animal or vegetable oil is an oil produced byhydrotreating palm oil (whole component) used as the raw material toremove the foreign substance. The hydrorefined gas oil corresponds to acommercially available JIS No. 2 gas oil which is used in a winterseason. The gas oil compositions of Examples 3 and 4 and ComparativeExample 2 were produced by blending these base oils in suitable amountsor using any of the base oils as the whole.

The additives used in these examples are as follows:

-   -   Lubricity improver: Infineum R 655 manufactured by Infineum        Japan Ltd. (active component: straight-chain alkylester mixture        containing a fatty acid as the raw material, average molecular        weight: 250 MW)    -   Detergent: alkenyl succinimide mixture    -   Cold flow improver: Infineum R240 manufactured by Infineum Japan        Ltd. (active component: ethylene-vinyl acetate copolymer        mixture, solvent: alkylbenzene) (melting point: −50° C. or        lower)

In Example 3, additives were added through predetermined steps, i.e.,steps wherein the lubricity improver was added and then sufficientlymixed and forced-stirred, and the cold flow improver was added and thensufficiently mixed and forced-stirred. Also in Example 4, additives wereadded through predetermined steps, i.e., steps wherein the lubricityimprover and the detergent were added and then sufficiently mixed andforced-stirred, and the cold flow improver was added and thensufficiently mixed and forced-stirred. In Comparative Example 2, onlythe cold flow improver was added. It was confirmed that these additivesused in these examples contained no solvent with a boiling point of 10°C. or higher.

Table 5 sets forth the blend ratio of the gas oil compositions thusprepared and the 15° C. density, 30° C. kinematic viscosity, flashpoint, sulfur content, oxygen content, distillation characteristics,content of normal paraffins every carbon number (CnP), content of normalparaffins having 20 to 30 carbon atoms (C20-C30P), value determined bydividing the total content of normal paraffins having 20 to 30 carbonatoms by the total content of hydrocarbons having 20 to 30 carbon atomsother than the normal paraffins, cetane index, cetane number, aromaticcontent, cloud point, cold filter plugging point, pour point, carbonresidue content of the 10% distillation residue, insoluble content andperoxide number after an oxidation stability test, wear scar diameterand water content of each composition.

The gas oil composition used in Examples 3 and 4 were produced byblending 60 percent by mass or more of the FT synthetic base oils as setforth in Table 5. Further, as apparent from Table 5, gas oilcompositions satisfying the characteristics as defined herein wereeasily produced without fail, in Examples 3 and 4 wherein the FTsynthetic base oils were blended within the range defined herein. On theother hand, as apparent from Comparative Example 2, where thecomposition did not have the characteristics prescribed in the presentinvention or was not admixed with the predetermined additives as definedin Steps 1 and 2 of the present invention, the gas oil compositions asintended by the present invention was not produced.

Next, the following various tests were carried out using the gas oilcompositions of Examples 3 and 4 and Comparative Example 2. All resultsare set forth in Table 6. As apparent from Table 6, the gas oilcompositions of Examples 3 and 4 are those with environment loadreducing properties, which are excellent in fuel consumption propertiesand low-temperature startability, compared with the gas oil compositionof Comparative Example 2 and thus are high quality fuels that canachieve at a high level excellent fuel consumption properties andlow-temperature startability in a winter season, that were difficult toachieve with the conventional gas oil compositions.

(Diesel Combustion Test)

The vehicle 1 described above was driven using each gas oil compositionunder a test mode shown in FIG. 1 to measure NOx, smoke and fuelconsumption. The results obtained using the fuel in Comparative Example2 were defined as 100, and the results of the other fuels wererelatively evaluated by comparison with the results of ComparativeExample 2 (smaller values indicate better results).

(Low-Temperature Startability Test)

Using the vehicle 1 and on a chassis dynamometer capable of controllingthe environment temperature, each of the gas oil compositions wassubjected to a test carried out at room temperature by (1) flashing(washing) the fuel system of a test diesel vehicle with a fuel to beevaluated; (2) draining out the flashing fuel; (3) replacing the mainfilter with new one; and (4) feeding the fuel tank with the fuel to beevaluated in a specific amount (½ of the tank volume of the testvehicle). The test was continued by (5) cooling rapidly the environmenttemperature from room temperature to −15° C.; (6) keeping thetemperature at −15° C. for one hour; (7) cooling gradually at a rate of1° C./h till reaching to the predetermined temperature (−25° C.); and(8) starting the engine after the temperature was kept at thepredetermined temperature for one hour. If the engine did not start evenafter 10 second cranking was repeated twice at an interval of 30seconds, the fuel was evaluated as “Not passed” at this moment. If theengine started while 10 second cranking was repeated twice at aninterval of 30 seconds, it was idled for 3 minutes and then the vehiclewas speeded up to 60 km/h over 15 seconds and driven at the low speed.When defects in operation (hunting, stumble, vehicle speed reduction orengine stop) were observed while the vehicle was speeded up to 60 km/hand driven at that speed for 20 minutes, the gas oil composition wasevaluated as “Not passed” at this moment. If the engine ran until theend without any defect, the gas oil composition was evaluated as“Passed”.

TABLE 4 Processed oil derived Highly from FT FT hydrogenated animal orsynthetic synthetic processed vegetable Hydrorefined base oil 3 base oil4 oil oil gas oil Density (15° C.) kg/m³ 782 792 814 765 831 Kinematicviscosity (30° C.) mm²/s 3.2 3.2 3.4 2.3 4.4 Distillation 10%distillation temperature 189.5 196.5 217.5 226.5 230.0 characteristics °C. 50% distillation temperature 247.0 256.0 272.0 249.5 292.5 90%distillation temperature 323.5 324.0 322.5 267.0 345.0 Sulfur contentmass % <1 <1 <1 <1 8

TABLE 5 Example Example Comparative 3 4 Example 2 FT synthetic base oil3 100 60 FT synthetic base oil 4 100 Highly hydrogenated processed oil10 Processed oil derived from animal or vegetable oil 10 Hydrorefinedgas oil 20 Density (15° C.) kg/m³ 782 792 771 Kinematic viscosity (30°C.) mm²/s 3.2 3.2 2.8 Flash point ° C. 60 58 58 Sulfur content mass ppm<1 <1 <1 Oxygen content mass ppm <10 <10 120 Distillation Initialboiling point 155.5 161.0 171.0 characteristics ° C. 10% distillationtemperature 189.5 196.5 217.0 50% distillation temperature 247.0 256.0264.0 90% distillation temperature 323.5 324.0 324.5 End point 358.0355.5 369.0 CnP C20 1.1 1.4 1.9 mass % C21 0.7 1.1 1.5 C22 0.4 0.7 1.1C23 0.3 0.3 0.7 C24 0.2 0.2 0.3 C25 0.1 0.1 0.2 C20-C30P 2.9 3.9 5.7C20-30 hydrocarbon content mass % 10.7 10.8 30.0 other than C20-30PC20-C30P/C20-C30 hydrocarbon content other than C20-30P 0.27 0.36 0.19Cetane index 70.8 70.8 85.7 Cetane number 65.5 64.0 80.9 Aromaticcontent Vol. % <1 3.6 <1 Cloud point ° C. −17.0 −11.0 −13.0 Cold filterplugging point ° C. −27.0 −25.0 −17.0 Pour point ° C. −35.0 −30.0 −22.5Carbon residue content of mass % 0.00 0.00 0.00 10% distillation residuePeroxide number mass ppm 0 13 1 Wear scar diameter (WS 1.4) μm 350 330460 Insoluble content mg/100 mL 0.1 0.1 0.6 Water content vol. ppm 12 1932 Lubricity improver mg/L 150 150 — Detergent mg/L — 100 — Cold flowimprover mg/L 150 150 150 Cetane number improver mg/L — — —

TABLE 6 Example Example Comparative 3 4 Example 2 Fuel consumption 88 84100 properties Vehicle exhaust gas NOx 93 98 100 Smoke 94 96 100Low-temperature −20° C. Passed Passed Not Passed startability test

Example 5 and 6, and Comparative Example 3

Base oils with characteristics set forth in Table 7 were blended toproduce gas oil compositions set forth in Table 8 (Examples 5 and 6 andComparative Example 3). FT synthetic base oils 5 and 6 are hydrocarbonmixtures produced by converting natural gas to wax or a middle fractionthrough FT reaction, followed by hydrotreating. The reaction conditionsfor each FT synthetic base oil varied. FT synthetic base oil 5 is a baseoil produced by isomerization positively carried out. FT synthetic baseoil 6 is a base oil resulting from a treatment wherein too much emphasiswas not placed on isomerization. The highly hydrotreated base oil is ahydrocarbon base oil produced by further hydrotreating a gas oil baseoil to further reduce the sulfur and aromatic contents. The processedoil derived from an animal or vegetable oil is an oil produced byhydrotreating palm oil (whole component) used as the raw material toremove the foreign substance. The hydrorefined gas oil corresponds to acommercially available HS No. 2 gas oil which is used in a winterseason. The gas oil compositions of Examples 5 and 6 and ComparativeExample 3 were produced by blending these base oils in suitable amountsor using any of the base oils as the whole.

The additives used in these examples are as follows:

-   -   Lubricity improver: Infineum R 655 manufactured by Infineum        Japan Ltd. (active component: straight-chain alkylester mixture        containing a fatty acid as the raw material, average molecular        weight: 250 MW)    -   Detergent: alkenyl succinimide mixture    -   Cold flow improver: Infineum R240 manufactured by Infineum Japan        Ltd. (active component: ethylene-vinyl acetate copolymer        mixture, solvent: alkylbenzene) (melting point: −50° C. or        lower)

In Example 5, additives were added through predetermined steps, i.e.,steps wherein the lubricity improver was added and then sufficientlymixed and forced-stirred, and the cold flow improver was added and thensufficiently mixed and forced-stirred. Also in Example 6, additives wereadded through predetermined steps, i.e., steps wherein the lubricityimprover and the detergent were added and then sufficiently mixed andforced-stirred, and the cold flow improver was added and thensufficiently mixed and forced-stirred. In Comparative Example 3, onlythe cold flow improver was added. It was confirmed that these additivesused in these examples contained no solvent with a boiling point of 10°C. or higher.

Table 8 sets forth the blend ratio of the gas oil compositions thusprepared and the 15° C. density, 30° C. kinematic viscosity, flashpoint, sulfur content, oxygen content, distillation characteristics,content of normal paraffins every carbon number (CnP), content of normalparaffins having 20 to 30 carbon atoms (C20-C30P), value determined bydividing the total content of normal paraffins having 20 to 30 carbonatoms by the total content of hydrocarbons having 20 to 30 carbon atomsother than the normal paraffins, cetane index, cetane number, aromaticcontent, cloud point, cold filter plugging point, pour point, carbonresidue content of the 10% distillation residue, insoluble content andperoxide number after an oxidation stability test, wear scar diameterand water content of each composition.

The gas oil composition used in Examples 5 and 6 were produced byblending 60 percent by mass or more of the FT synthetic base oils as setforth in Table 8. Further, as apparent from Table 8, gas oilcompositions satisfying the characteristics as defined herein wereeasily produced without fail, in Examples 5 and 6 wherein the FTsynthetic base oils were blended within the range defined herein. On theother hand, as apparent from Comparative Example 3, where thecomposition did not have the characteristics prescribed in the presentinvention or was not admixed with the predetermined additives as definedin Steps 1 and 2 of the present invention, the gas oil compositions asintended by the present invention was not produced.

Next, the following various tests were carried out using the gas oilcompositions of Examples 5 and 6 and Comparative Example 3. All resultsare set forth in Table 9. As apparent from Table 9, the gas oilcompositions of Examples 5 and 6 are those with environment loadreducing properties, which are excellent in fuel consumption propertiesand low-temperature startability, compared with the gas oil compositionof Comparative Example 3 and thus are high quality fuels that canachieve at a high level excellent fuel consumption properties andlow-temperature startability in a winter season, that were difficult toachieve with the conventional gas oil compositions.

(Diesel Combustion Test)

The vehicle 1 described above was driven using each gas oil compositionunder a test mode shown in FIG. 1 to measure NOx, smoke and fuelconsumption. The results using the fuel in Comparative Example 3 weredefined as 100, and the results of the other fuels were relativelyevaluated by comparison with the results of Comparative Example 3(smaller values indicate better results).

(Low-Temperature Startability Test)

Using the vehicle 1 and on a chassis dynamometer capable of controllingthe environment temperature, each of the gas oil compositions wassubjected to a test carried out at room temperature by (1) flashing(washing) the fuel system of a test diesel vehicle with a fuel to beevaluated; (2) draining out the flashing fuel; (3) replacing the mainfilter with new one; and (4) feeding the fuel tank with the fuel to beevaluated in a specific amount (½ of the tank volume of the testvehicle). The test was continued by (5) cooling rapidly the environmenttemperature from room temperature to −15° C.; (6) keeping thetemperature at −15° C. for one hour; (7) cooling gradually at a rate of1° C./h till reaching to the predetermined temperature (−25° C.); and(8) starting the engine after the temperature was kept at thepredetermined temperature for one hour. If the engine did not start evenafter 10 second cranking was repeated twice at an interval of 30seconds, the fuel was evaluated as “Not passed” at this moment. If theengine started while 10 second cranking was repeated twice at aninterval of 30 seconds, it was idled for 3 minutes and then the vehiclewas speeded up to 60 km/h over 15 seconds and driven at the low speed.When defects in operation (hunting, stumble, vehicle speed reduction orengine stop) were observed while the vehicle was speeded up to 60 km/hand driven at that speed for 20 minutes, the gas oil composition wasevaluated as “Not passed” at this moment. If the engine ran until theend without any defect, the gas oil composition was evaluated as“Passed”.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

TABLE 7 Processed oil Highly derived from FT FT hydrogenated animal orsynthetic synthetic processed vegetable Hydrorefined base oil 5 base oil6 oil oil gas oil Density (15° C.) kg/m³ 786 782 814 765 831 Kinematicviscosity (30° C.) mm²/s 3.7 4.0 3.4 2.3 4.4 Distillation 10%distillation temperature 200.5 229.0 217.5 226.5 230.0 characteristics °C. 50% distillation temperature 275.5 299.0 272.0 249.5 292.5 90%distillation temperature 329.0 339.5 322.5 267.0 345.0 Sulfur contentmass % <1 <1 <1 <1 8

TABLE 8 Example Example Comparative 5 6 Example 3 FT synthetic base oil5 100 60 FT synthetic base oil 6 100 Highly hydrogenated processed oil10 Processed oil derived from animal or vegetable oil 10 Hydrorefinedgas oil 20 Density (15° C.) kg/m³ 786 793 782 Kinematic viscosity (30°C.) mm²/s 3.2 3.3 4.0 Flash point ° C. 64 62 71 Sulfur content mass ppm<1 <1 <1 Oxygen content mass ppm <10 <10 120 Distillation Initialboiling point 181.0 178.5 175.5 characteristics ° C. 10% distillationtemperature 200.5 196.5 229.0 50% distillation temperature 275.5 256.0299.0 90% distillation temperature 329.0 323.5 339.5 End point 359.0358.5 369.0 CnP C20 1.6 1.7 3.2 mass % C21 1.3 1.5 3.4 C22 0.9 1.2 3.1C23 0.5 0.7 2.6 C24 0.2 0.4 2.6 C25 0.1 0.1 1.9 C20-C30P 4.8 5.9 3.1(C24-C25)/C24 0.50 0.75 0.27 (C22-C23)/C22 0.44 0.42 0.16 (C20-C21)/C200.19 0.12 −0.06 C20-30 hydrocarbon content mass % 15.5 15.1 16.3 otherthan C20-30P C20-C30P/C20-C30 hydrocarbon content other than C20-30P0.31 0.39 0.19 Cetane index 79.0 68.5 91.6 Cetane number 67.8 68.3 80.9Aromatic content vol. % <1 3.6 <1 Cloud point ° C. −5.0 −7.0 −3.0 Coldfilter plugging point ° C. −13.0 −12.0 −4.0 Pour point ° C. −17.5 −17.5−5.0 Carbon residue content of mass % 0.00 0.00 0.00 10% distillationresidue Peroxide number mass ppm 1 12 2 Wear scar diameter (WS 1.4) μm360 360 460 Insoluble content mg/100 mL 0.1 0.1 0.7 Water content vol.ppm 18 18 47 Lubricity improver mg/L 150 150 — Detergent mg/L — 100 —Cold flow improver mg/L 150 150 150 Cetane number improver mg/L — — —

TABLE 9 Example Example Comparative 5 6 Example 3 Fuel consumption 92 89100 properties Vehicle exhaust gas NOx 98 97 100 Smoke 91 97 100Low-temperature −10° C. Passed Passed Not Passed startability test

1. A gas oil composition comprising a gas oil composition selected fromthe group consisting of the following gas oil compositions (B) andadditives added in accordance with the following Steps 1 and 2: [I] gasoil compositions (B) comprising an FT synthetic base oil in an amount of60 percent by volume or more on the basis of the total amount of the gasoil composition, with a sulfur content of 5 ppm by mass or less, anaromatic content of 10 percent by volume or less, an oxygen content of100 ppm or less, a density of 760 kg/m³ or greater and 840 kg/m³ orless, a 90% distillation temperature of 280° C. or higher and 350° C. orlower and an end point of 360° C. or lower in distillationcharacteristics, an insoluble content after an oxidation stability testof 0.5 mg/100 mL or less, an HFRR wear scar diameter (WS1.4) of 400 μmor smaller, a cloud point of −5° C. or lower, a cold filter pluggingpoint of −20° C. or lower, a pour point of −25° C. or lower, a totalcontent of normal paraffins having 20 to 30 carbon atoms of 2 percent bymass or more and less than 4 percent by mass, a value determined bydividing the total content of normal paraffins having 20 to 30 carbonatoms by the total content of hydrocarbons having 20 to 30 carbon atomsother than the normal paraffins of 0.2 or greater and 0.6 or less, and arelation in the content of each of normal paraffins (CnP) having 20 to25 carbon atoms defined by C20P>C21P>C22P>C23P>C24P>C25P; and (Step 1) alubricity improver comprising a fatty acid and/or a fatty acid ester isadmixed in an amount of 20 mg/L or more and 300 mg/L or less in terms ofthe active component with the gas oil composition by line-blending,forced-stirring or leaving to stand for a sufficient time; and (Step 2)a cold flow improver comprising an ethylene vinyl acetate copolymerand/or a compound with a surface active effect is admixed in an amountof 20 mg/L or more and 1000 mg/L or less in terms of the activecomponent with the gas oil composition by line-blending, forced-stirringor leaving to stand for a sufficient time.
 2. The gas oil compositionaccording to claim 1, wherein the gas oil composition is admixed with200 mg/L or more and 500 mg/L or less of a detergent comprising apolyether amine compound, a polybutenyl amine compound, an alkenylsuccinamide compound, or an alkenyl succinimide compound byline-blending, forced-stirring or leaving to stand for a sufficienttime, in a step added between Steps 1 and
 2. 3. The gas oil compositionaccording to claim 1, wherein the lubricity improver, detergent and coldflow improver each contain a solvent containing no chemical substancewith a melting point of 10° C. or higher.
 4. The gas oil compositionaccording to claim 1, wherein the gas oil composition has a peroxidenumber after an accelerated oxidation test of 50 ppm by mass or less, akinematic viscosity at 30° C. of 2.5 mm²/s or greater and 5.0 mm²/s orless, a cetane index of 45 or greater and a water content of 100 ppm byvolume or less.
 5. The gas oil composition according to claim 2, whereinthe lubricity improver, detergent and cold flow improver each contain asolvent containing no chemical substance with a melting point of 10° C.or higher.
 6. The gas oil composition according to claim 3, wherein thegas oil composition has a peroxide number after an accelerated oxidationtest of 50 ppm by mass or less, a kinematic viscosity at 30° C. of 2.5mm²/s or greater and 5.0 mm²/s or less, a cetane index of 45 or greaterand a water content of 100 ppm by volume or less.
 7. The gas oilcomposition according to claim 2, wherein the gas oil composition has aperoxide number after an accelerated oxidation test of 50 ppm by mass orless, a kinematic viscosity at 30° C. of 2.5 mm²/s or greater and 5.0mm²/s or less, a cetane index of 45 or greater and a water content of100 ppm by volume or less.